Diarrhea. You'd think after having three kids, I'd be used to it, but after they get to be about two, and having suffered increasinly worse nausea with each pregnancy, it turns my stomach every time.
I have to just stand the affected child in the shower, clothes and all, to deal.
Vomit I can do, even vomit caught in long hair, which is pretty gross.
But I can't do diarrhea.