Half-Cheek-Squeak
A fart (usually in public) tried to be kept silent, by leaning to one side, and squeezing the butt cheeks together. However, failing to be silent, but instead of being a full blown butt trumpet, turns out to be a long winded high pitched squeak. Also causing it to be WAY funnier/more embarassing.
*Dude, Tom leaned over in class today and totally let out a half-cheek-squeak. It sounded like someone opening a balloon!*