Rainbow wank Share definition Flag When you masturbate for so long there is blood from chaffing, by the time you ejaculate the semen will be mixed with blood. Dude I was masturbating for so long last night I gave myself a rainbow wank. Rainbow wank by bunkbuddies May 9, 2010 0 0 Get merch Get the Rainbow wank mug. Buy Now — $32.95 See more merch