Evil and cheerful is hilarious combination. Evil-doings delivered with a smile. I love the 'bad' traits myself and I do use them except, like @LaBlue0314, I nuke the kleptomaniac trait like it was a hoard of wasps chasing me. Everywhere I come across it it gets edited out of existence but I do trade it with a 'bad' trait to even things out.
That being said I have had some humorous (for me) reactions to those bad traits when I was first starting to play Sims 4. But first I have to mention that the very first Sim I created and is a founder of my main saved game, so to speak has both the clumsy and the now named erratic trait, she is also family oriented. I chose the erratic trait because her story is that she has had and does have mental problems and the clumsy trait because, well, she is clumsy :wink: Another Sim that is my favorite has the hot-headed trait and I love it. It suits him to the tee. I really don't consider those 3 traits along with f.i. squeamish, vegetarian, non-committing as a bad trait.
Now, the first time I encountered the hates children trait was in the maid that was first hired by my founder Sim. After one Get to Know, my Sim's hubby found out that she had that trait and I was so startled that the poor lady got the sack on the spot and out on her rear in two shakes of a tail. She didn't even get to finish her choirs. Which is why my game has now 2 maids (well 3rd popped up when Sulani appeared). I also didn't have one Sim get a job because she has the lazy trait and I did stay away from both mean and evil Sims until I decided that one evil Sim would be a perfect spouse for Salim Benali and when the Roomies' new roomie started eating out the trashcans my eyebrows got a bit of an exercise. Now this was before I realised that traits don't really matter and have a negligent impact on Sims lives and personalities. Personally I wish it did have more impact but I do like all traits as it gives me more variety, personality wise.
Oh and a little factoid, the maid with the hates children trait has also the evil trait and non-commitment trait. The poor lady. I really have to add her to my rotation one of these days.
There are traits that I somewhat avoid when giving Sims (either in CAS or when they are growing up) new traits, like unflirty and jealousy, although it was interesting when a newly baked father became jealous when his baby mama payed more attention to the toddler than him and threw a tantrum. I see some interesting story for them in the future. But jealousy can be a pain for the tenseness and the unflirty is challenging when trying to court Sims with that trait. I do just treat Sims with the unflirty trait as asexual and leave them be. Like Raj Rasoya.
But if I encounter them in Sims like pre-mades, NPCs or homeless townies I leave them be even if they become part of a rotational household and I don't let that stop me. If I like a Sim that has those traits they get added regardless.