Hope you'll forgive me for just finding out about traits and jumping in here; I know I'm a little late.
First, thanks to @Rowenaenchantress for her most excellent table listing all the relevant mods for hexagonalbipyramid's traits! An excellent resource, as was said earlier in this thread.
Second, thanks to everyone above for their thoughts already and especially to @sunrader for starting the thread. It's a worthwhile topic!
Third, I went through and picked out the traits I plan to use in my game (of course, I'll use the traits randomizer to assign them). Here are some ideas I have about their implementation; most of my ideas were what I thought I could implement in playstyle. Some may be moddable as well, so I may cross-post a link in the Would Like to See thread or possibly just condense a version of the bits that seem easiest to mod, to post there. Note that if Rowena currently mentions a mod for a given trait in her table, I assume in my thoughts below that I'll already have that mod, so I won't specify any change that a trait-based mod already creates. Also, there are just a few more traits I plan to use in my game that I haven't listed here, just because currently I don't have any good ideas for implementing them in a meaningful way!
Adventurous: Especially attracted to the obstacle course and dance sphere. Delights in public woohoo and camping, always wants to find the secret lot on a vacation hood---particularly so they can meet Bigfoot, always wants to Learn to Teleport (or maybe some kind of needs boost when they have teleported). Could be modded to be much more likely to escape from crib as a toddler (that idea is directly cribbed from Early Pleasantview's blog, though she suggested it for the Brave trait).
Athletic: Prefers the dance sphere to regular dancing; always wants to Learn Tai Chi. Could be modded to always have Go Jogging enabled.
Avant Garde: Add decor, particularly nonclassical art and other deco, to home; dress as edgily as possible; visit contemporary art museums (if any) in the hood frequently.
Bookworm: Prefer book-based skilling to any other kind for the same skills; prefer to Do Research in Uni (vs assignments and term papers). Could be modded to learn faster when skilling from books, like a mini version of the Books for Learning effect, and/or to always have access to Discuss Book perk of Film/Lit hobby.
Can't Stand Art: Never visit art museums (could use VC to ban them from art museum lots), no art in the home (including kitschy stuff) or at least in their room if they are teen to younger or have roommates, never wear the edgiest clothing available.
Charismatic: Could be modded to have the Simply Influential OFB perk.
Childish: Doesn't use birth control, attracted to playing with any child (dollhouse), toddler (rabbit and any other Play With interaction), or baby toys (dangle toys on the DangleMonster) on the lot. Could be modded to be especially likely to Read To any child on the lot (so they get to do the voices)---even if unrelated.
Clumsy: Could be modded to gain Dance and Pool skills slower and to have worse luck fishing, or even to be injured (sharp Comfort loss?) while fishing. Perhaps could also be modded to never do a graceful dive regardless of Body skill level. Wonder if there's a way to also mod them to always lose (fall first) at the BV Log Roll!
Couch Potato: Reject all outings (so they can go/stay home), prefer book-skilling to any other kind (like Bookworm), don't automatically go to uni classes (because would rather stay home and Do Research or skill from books). Could be modded to sit more often instead of standing, maybe be exempted from mods that stop sims from frequently Relaxing on beds.
Disciplined: Always uses birth control if desired number of kids (ACR) is reached. Wants to learn Tai Chi for the energy boost. Could be modded to wake up on their own if Energy is above a certain (not necessarily high) level whenever their carpool/bus arrives, as well as to never overeat (could be added to mods that already ensure that Active or Fit sims never overeat).
Dislikes Children: Never participates in Read To interaction with children; never does Play With with kids' toys; avoids children on community lots (and playgrounds altogether---I'll use the VC to ban them from my one dedicated playground).
Eco-Friendly: Somewhat prefer vegetarian dishes as lighter on the environment (so, if it's their turn to cook they'll always make those but won't refuse to eat what someone else cooks); prefer cabin or camping accommodations on vacation; lose comfort while driving cars (as Early Pleasantview suggested)...heh, unless driving a
Prius (or other cc electric vehicle).
Evil: Yell At household pets and strays whenever there aren't others around to see; could be modded to get a mood boost if pickpocketing or fire or burglary happens while they are around, or if the Evil Witch appears; maybe could be modded to get a mood boost from talking to the Evil Witch and a mood hit from seeing or talking to the Good Witch?
Good: Always Report Foul Play even if tired, in the middle of a date, or needing to get home; always feed strays. Could be modded to take a mood hit if pickpocketing, fire, or burglary occurs while they are around, or if the Evil Witch appears; maybe could be modded to get a mood boost from talking to the Good Witch?
Grumpy: Occasionally mean to pets and sims at random, even if technically a Nice sim.
Handy: Study Mechanical a couple levels higher than they have visible Wants for (I'm a wants-based player), or could be modded to learn Mechanical faster from tinkering than the average sim. (Is that something Tinkering sims already do?)
Hates the Outdoors: Refuses water balloon fights (I already have a mod to allow those only outside); won't fish or build snowmen unless forced. Complains when asked to garden or rake leaves. Could be modded to have very sharp Comfort drop (and poor Energy restoration) if sleeping in tents or hammocks and to get no comfort benefits from sitting around a campfire; I wonder if it could be modded to prevent them from fishing or building snowmen ever.
Hydrophobic: Will avoid going out in rain or snow, to the point of taking vacation time if available. Never lives on a beach lot or chooses beachfront lodging (same with ponds). Never plays with or owns fountains (woe to the date gifter who drops one off!); won't fish, build snowmen, or water plants in any way. Could be modded to hate using public toilets (might have puddles from the last user); maybe could be similarly modded as above to never fish or build snowmen or water plants.
Loner: Never joins Greek Houses or is in the Secret Society; focuses on skilling vs. friending for work; when has to make friends, strongly prefers the phone to getting together with the sim.
Loves the Outdoors: Always builds snowmen, loves water balloon fights, fishing, gardening, and even likes raking leaves. Goes outside in storms (just to experience them---can you Watch Clouds when it's raining)? Strongly prefers camping or cabin lodging when on vacation. Probably owns a tent, if space. Maybe could be modded to do the M&G deep-breath animation more often; I've actually modded that one out of my game already but might be okay if there's a sim-specific reason that some still do it.
Lucky: Improved odds when I roll for ROS outcomes; always gets a genie wish (usually I only give wishes to sims who roll the want after a lamp appears). Could be modded to get reduced odds of catching boots while fishing as well as improved odds at Cheating Death and improved odds of finding something valuable, including maps, when Digging for Treasure.
Night Owl: Takes afternoon siestas to be able to stay up late.
Rebellious: Often late to work or school; often calls in sick; enjoys public woohoo. Treat as always disliked by the Headmaster, so that it would have to be other sims in the household who deal with him. Could be modded to allow Streak interaction.
Sailor: Seagoing decor in their home, maybe a preference for a nautical theme (or just blue and white) in dressing.
Schmoozer: Would always try and Give Tour or otherwise deal with the Headmaster (who still might not like them unless that is possible to mod). Usually on time for work/school. Uses the Call Friends function (from Pescado's phonehack) to keep up all their social relationships, even if not a Popularity sim and even if not as Outgoing as my sims who'd normally do that (that is, most of my sims do not use Call Friends). Could be modded to have the Assess Mood OFB perk.
Snob: Continually want to upgrade their stuff (maybe give a Fortune secondary, if not already Fortune, and fulfill all their buy-stuff wants that have a minimum value). Buy clothes for all family members living with them in a self-serving way (dress them the way they feel reflects best on them). Always pick the richest/most prominent sim on the lot to talk to; always get the most expensive vacation lodging they can afford; usually seek to live in the area that has the most prominent sims living there already. Won't engage in Public Woohoo unless three bolts AND they're pretty sure the lot is not one that anyone "important" would come to.
Social Butterfly: Always joins a Greek House, if available. Throws parties more frequently than their wants would indicate (or, if a Popularity sim, at least as often as their wants indicate), and makes a special effort to vary their guest list; uses Send/Check Email function on Monique's computer daily if lazy or very shy, or otherwise personally goes out to community lots daily on some pretense or other ("I'll get the groceries, sure! See ya!")
Socially Awkward: Usually uses Chat (choice on the other sim) as their socialization preference and never rotates the socials (you know, among three different ones, so the other sim doesn't get bored). Chooses awkward moments to try to approach other sims, like when they're already busy, and waits anyway until the action drops out of queue. Could be modded to be unable to Tell Joke or do the AL Greets.
Supernatural Fan: Always wants to meet Bigfoot, Learn to Teleport, and obtain the voodoo doll and mystical Far East scroll.
Supernatural Skeptic: Never wants to do any of the above.
Unlucky: Poorer odds when I roll for ROS outcome; never get any genie wishes even if their household finds a lamp. Could be modded to get increased odds of catching boots while fishing as well as reduced odds at Cheating Death and reduced odds of finding something valuable, including maps, when Digging for Treasure.
Vehicle Enthusiast: Prioritize buying a new, better car as often as possible, even just changing colors if there's no nicer car to buy. Maybe keep old cars in inventory instead of selling them. Never uses Call Taxi or Walk to Lot (unless on vacation). Could be modded so that these sims work faster on the junk car faster or make more money from it (I already have mods that slow progress on the junk car and make it sell for less, but of course this reverse version would have to only be true for these certain sims).
Workaholic: Never takes paid leave or misses school and has a high chance of not taking sick leave either. Until uni, always does HW. During uni, always does at least their term paper. Never sells an OFB business at lower than level 8 and never hires a manager for any business they own.
Whew! Looking forward to any and all comments on these, including about moddability---I've never been a modder.