A buttwink is when a
person flexes their anal sphincter, causing their anus to visibly contract, effectively "winking" with their asshole. Buttwinking can be performed as an obscene gesture, or in a sexual context it can be either a sign of affection or a greeting.
To buttwink, simply use the same muscles used to defecate to
flex your anus.
This act should not be confused with mooning (merely exposing your anus) since buttwinking is considerably more
rude.
As Sensei Doug walked to his dojo, the
rude employees of a strip mall store lowered their drawers, pointed their behinds towards the
window, and contracted their assholes to buttwink at the passing martial
artist.