protean shake Share definition Flag A guys cum. Cum is suppose to be made of protean, so it is a joke, relateing to a mileshake made out of cum. A girl gave her boyfriend oral sex, when he came in her mouth, she drank a protean shake. protean shake by Tim Fackler December 15, 2008 0 0 Get merch Get the protean shake mug. Buy Now — $32.95 See more merch