Ironically, when I was in middle school it was a common joke to lick people’s elbows when they weren’t paying attention. The joke was that they might not notice it at first, since elbows supposedly had few nerve endings.
It was about as common as untying people’s shoe laces, for a while. Meaning: very common.
I agree, and I propose a second reason: it is too easy (for my dumb self, at least) to not realize the seat is up, try to sit down, and go for an unexpected swim