cheek flapper
To expell gas from one's anus with such force that both sides of his/her buttox slap together to create a distinctly audible, and occasionally painful, vibration.
During the awkward silence on his date, John let forth such an intense cheek flapper that the silverware on the table rattled.
Flapper cheeks
But cheeks that are so saggy that they can make that person fly.
I once saw some damn flapper cheeks!