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The act of giving a male oral pleasure by placing his penis between your upper lip and the bottom of your nose and moving your head side to side.
Male 1: Dude, you know that chick I banged last night? She gave me a sweet mustaching before I finished!

Male 2: Wow you must have a tiny dick!
by RideMaLightin' November 17, 2011
An occupational hazard caused by using cheap staplers: almost like resistoring or telephoning, where the staples do not complete "bite" into the other side of a document, except the staples take on a more rounded form, like a handlebar mustache.
Why does this effing stapler keep on mustaching on me?
by pentozali February 14, 2011