Placing one's puckered butthole against someone else's face. First, spread your butt cheeks so as to fully expose the butthole. Next, slowly place the butthole up against someone's face. Finally, let go of the butt cheeks, so that they slap the person's face and flutter like a butterfly's wings.
A fart that travels superiorly, causing audible labial vibration. Most likely to occur when a female farts while reclined in tight pants. Not to be misconstrued as a queef traveling superiorly causing labial vibrations; women don't fart during sex.
While watchingthe game he asked "what was that sound and why are you giggling?". She replied "a butterfly kiss".