Yes, singing and the parenting skill. Not every sim wants to be a parent but it doesn't stop them from forever browsing parenting forms, even the ones who don't like children. If anything, I would want the "Hates Children" sims to have bad parenting skills if they end up becoming one. Or they sing once and then they never stop. Well, thanks to mods those things have calmed down. I let my sims do everything autonomously and it can be a pain when there's something they latch onto that you don't want them to.
I would also love for some of them to stay bad cooks forever. How else am I going to host "pufferfish" dinner parties if the food quality is too good to kill anyone? >:)