Rat 'Stache Share definition Flag A moderate amount of facial hair protruding above the upper lip. More a reflection of abandoned hygiene than maturity/suaveishness. "Dude, buy a Bic. You got cheesey dust in your rat 'stache." Rat 'Stache by Combatbat February 10, 2005 0 0 Get merch Get the Rat 'Stache mug. Buy Now — $32.95 See more merch