A usually somewhat embarrassing thing that could happen for a few reasons.
1. You are a young
infant with no bladder control
2. You are an elderly citizen who has the same excuse and the infant.
3. You held your pee in for too long.
4. You have a fetish, and
pee yourself for enjoyment ( ͡° ͜ʖ ͡°)
5. You are an actor on
pornhub who's job is to piss their pants/shorts/panties/underwear for others' sexual amusement