periscope fart

When you press your butt against a hard, flat-surfaced chair and fart, but there is no place for the gas to escape except up the crack of your ass. and out at the top.

Dude, I laid the biggest periscope fart in detention. I press my butt cheeks against the hard chair and farted and the gas came bubbling up the crack of my ass and peeked out at the top!