When you have to go the bathroom so badly you pee a little into your clothing to relieve some of the pressure. If you're at this stage then odds are very high you're not gonna make it to the bathroom in time.
"Dude! Did you see the back of Kayla's skirt when she rushed out?"
"Hell yeah! She must have let loose a gully washer during class."
"And did you see her after she ran into the hall? She, like, just started pissing onto the floor and it was, like, wierd!"