foulfist Share definition Flag Verb. When a person in the brewing industry dips their hand into a yeast cake and either a.) punches the boss directly in the face, or b.) shoves the fist up the boss's ass. Lars was giving him trouble, so Darren had to foulfist him. foulfist by Dr. Yeti October 6, 2006 0 0 Get merch Get the foulfist mug. Buy Now — $32.95 See more merch