Self-proclaimed daddy Andy Cohen hosted The D Train stars Jack Black and James Marsden this week on Watch What Happens Live!, where the two stars had to play "School of Cock."

Black and Marsden were shown a series a crotch shots and had to guess whether it was one of their own bulges or some other celebrity's basket.

Related: Jack Black And James Marsden Take Bromance To The Bedroom In "The D Train"

Given how Black and Marsden's characters become intimately familiar with each other's bodies in D Train, we figure they've become experts on their lumps.