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.
Flappers of the 1920s were young women known for their energetic freedom, embracing a lifestyle viewed by many at the time as outrageous, immoral or downright dangerous.
Mavericker: NIPP you look like you belong in the 1920s.
Nipp: What do you mean?
Mavericker: You look like a FLAPPER GIRL.