The only trait I avoid and will change if I start playing a sim who already has it is the kleptomaniac trait. The ironic thing is that I absolutely loved playing with this trait back in Sims 3, but find it extremely annoying in Sims 4. I can't even tell you the number of times in the past that other sims (that I was not playing) would make things vanish that belonged to my playable sims. Other than that I don't have any issues with any of the negative traits in the game.