Worst traits

[Cheezey]

Rebellious: Pointless as an adult.
Coward: The constant fainting. 
Absent Minded: It's a chore to get a sim with this trait to do anything. And I like my sims to be self-sufficient.
Loser/Unlucky: Does it really need an explanation?   
Light Sleeper: Sleeping through the night is hard, I would know.
Dislikes Children: All of my sims are Family Oriented.
Slob: Makes a mess every time! But it makes the maid earn her pay.

There's more, but I'll stop my rant there. What's the point of these bad traits anyway? Didn't EA understand that they'd be rarely used?

One reason was to give people the option to tweak their sims for unpleasant personalities, for those who enjoy watching sim drama.  Another reason is that they can be used as a penalty for not training your sim's toddlers or letting your sim's children and teens go through school with bad grades.  While cheats can change those, it creates more of a challenge for players who prefer that aspect in their game.

Regarding loves the outdoors, yes, I know exactly what you mean!  The water slip and slide thing from Generations will also attract them like a magnet.

[Bugdozer]

There's more, but I'll stop my rant there. What's the point of these bad traits anyway? Didn't EA understand that they'd be rarely used?

One of the most fun households I ever played was one I filled with Sims with entirely bad traits. Put free will on high and watch the antics ensue! I made them even more bad tempered by putting TVs and radios in all the rooms with beds in so they got woken up a lot, and also gave them one less bed than the number of people living in the house 
OK, maybe I have some bad traits myself...

[InfiniSimmer]

For me, Absent Minded isn't so bad. I have a teen who's absent-minded and she's fine, even on the honor roll. I use Flirty when I'm creating a Sim meant specifically to marry another Sim and I want to get the relationship up fast.

Cowards: Personally, I simply can't stand a coward.
Grumpy: An annoying random mood depletion after getting up.
Dislikes Children: Difficult. There are a lot of children in the game.

[Iggyman]

I like most of the traits, but by far way far the most annoying for me is absent-minded.  I hate how they stop doing something in mid-action. Or when they are  standing in a room wondering how they got there. Meh... that's really annoying.

I also don't like, hotheaded and how they get any conversations gone awry or even the slightest negative moodlet will send them into a boiling rage. I hate that. Loser and Coward.
Neurotic gets on my nerves everytime, and how the freak out over every little thing. I always tried to avoid any contact with Neurotic sims, but I don't dislike that trait..
I love Diva only because I always want my sims to be the center of the universe. and how they are always likely to slap Sims when being insulted. Just awesome to watch.
 

[pumpkincarnival]

I think the coward one might be my least favorite.  I get tired of them collapsing all over the place 

Mean-spirited is also one that gets on my nerves after awhile.  It's fun at first, but then I get tired of it and want them to just get along.

[MoirailZoned]

My starting Sim got Bianca Rubble to move in... Ugh. She's a Slob, Absent-Minded, and a Coward. My Sim is Proper, so that posed some annoying problems and an unwanted drop in their relationship. I don't mind Absent-Minded on her too much, since I don't control the previous-townsies. I just leave them to their own devices. But, when Absent-Minded is on a Sim I'm actually controlling, it's so annoying to get things done, especially if they're the only one home. Coward has posed some problems with her, because she's fainted in front of doors before (esp. the bathroom) and caused some annoyance to both myself and the Sims trying to get into the bathroom.
One of my Sim's Imaginary Friends is Mean Spirited, which has brought me to questioning whether or not I want to make her real... Their relationship has already gone down a lot, and I really don't think it'd be worth it.

[nemmi]

Hopeless romantic bc I don't want Andy dating at all

[HSmith2016]

My one Sim has both Green Thumb and Hates the Outdoors personalities. That's an interesting combination. But it drives me nuts when she goes outside for any reason (even to go to work) and always gets the wish to Go Inside. Her mood instantly goes down any time she steps outside. It was fun at first, but now it's just annoying.

[BlairAragon]

Technophobe, Mean spirited, Clumsy and Hate the Outdoors.

[sharpsiren]

Never nude! Absent-minded. Grumpy.

[Magz from Oz]

Grumpy is a really bad trait if you're using that character in screenshots.  They scowl all the time!

[Happy]

I hate coward and light-sleeper the most. I enjoy the well-rested moodlet and I don't get what good is the light-sleeper trait for sims. Coward is the worst because they faint in the dark, in a fire (very dangerous!) and robberies. In that case I can't call the police to arrest the burglar. It is the most annoying