People who use a toilet without leaving it in a decent state. In the absence of a good and honest reason, should these people be allowed to call themselves adults? No, I don't think that they should be.
Share gross toilet stories here.
I once spent spent an evening, alone in the toilet cubicle of a night club, lying on the floor which was already soaked in other people's wee, vomiting every so often. What a pleasant night's dancing that was.