For a certain cause such as laughing, fear, or waiting to long you pee without warning into your pants making a visible stain where your pee was running depending on what your wearing.
i had a friend over, he was playing a one-player game. i stood behind him, and i just started peeing. "oh my god, i just peed my pants" i said. my friend didn't belive me so i showed my jeans. i like peeing myself