The worst trait is Meanspirited for me.
I have meanspirited sim and he enjoys pointing his family with his finger for insulting. But good point is that meanspirited sims can BEAT UP the burglars.
The 2nd worst trait is inappropriate.
I think they have the better ability to make love more than flirty or hopeless romantic sims. It's almost unable to guess what they will do the next action. Sometimes, they act like the meanspirited or hotheaded sims, sometimes, they act like the flirty or hopeless romantic sims. They can kiss with other strangers.