The act, or more aptly; The rather unfortunate act of reaching climax at the exact moment a plane comes crashing through your roof. For this act to be properly performed, your family* must be in the next room when the plane reduces your masturbating ass to charred dust.
*Your family obviously excludes your sister. Who should be at my house working on taming her gag reflex.
"Did you hear about that guy who had a Planegasm? His sister gives GREAT head now!"
"So your whole family was across the room when she came? I'm so sorry to hear that..."