Infatuation, does that count? I see this as the most annoying status effect on a Pokémon, because I can never seem to get an attack in after having one of my Pokémon fall in love. >_>;
If not, then having my Pokémon paralyzed would be my most hated. For some reason I just have terrible luck with it. It has a 30% chance of happening, yet it seems to occur more than it should. :\ While, when I have my opponent paralyzed, it only occurs to them every once in awhile. On top of it all, it slows down your speed, and in most cases, that isn't a good thing; especially if you like to have the first move.