cumstain Share definition Flag the term used to describe a girlfriend or boyfriend who was used mainly for sex. Well now that they broke up, shes just a cumstain. Maybe I should hook up with her next, then ditch her after Ive finished. cumstain by falconpunchdude April 5, 2011 0 0 Get merch Get the cumstain mug. Buy Now — $32.95 See more merch