The Act of Something or Someone being in the State of Such Concentration and Hilarity, That they have an Involuntary Eruption of Urine; To the Effect that their Pants are Completely and Utterly Soaked in Their own Urine.
"Mitch Hedberg was Piss-Pants Funny!"
"Dude, That guy Falling down the Stairs was Bad, But Piss-Pants Funny."
Man, Yo Momma is So Ugly, She's Piss-Pants Funny..."
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.