Taking a bowel-emptying crap in one's shorts, usually in response to being startled. The complete and sudden evacuation of one's bowels into their underwear or shorts.
"Dude, when that car came at me I filled my shorts!"
"Yeah, I can smell it!"

"BOO!"
"Damn dude, you made me fill my shorts you bitch"
by Mahalollama September 13, 2009
Get the Fill my Shorts mug.