When you don't shave your grundle and ball sack for a couple months then do an activity so it is sweaty and smells like shit. Then you find a person repeatedly smack them in the face with your sack and rub your grundle all up on there face while getting a rusty trombone. When you are about to cum you turn and bust on there upper lip getting the pubes to become a facial mustache.
Josh C gave his dad a smackastache and pooped in it to match his hair color.
by TheDumptruckBandit April 19, 2009
5 Words related to smackastache

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