Tin Cap Share definition Flag The act of withdrawing the penis during male/female intercourse prior to climax and directing the male ejaculate towards the armpit area of the female partner. "My boyfriend and I don't want to get pregnant so he likes to Tin Cap sometimes. Tin Cap by carlzebra January 16, 2009 0 0 Get merch Get the Tin Cap mug. Buy Now — $32.95 See more merch