The highly velocitized escape of gaseous matter via the rectum whereby the rim of the sphincter is first inadvertently puckered inward, then violently blown outward causing a momentary flapping as the blast escapes then subsides. The turbulent build up generally occurs as the sphincter is squeezed shut for extended periods. First dates, group meditations, and solemn religious ceremonies frequent such occurrences.
Damn that girl was so sweet I just wanted to sidle up closer, but for that bottled up rim flapper.
by Paco February 27, 2004