Belgian Blowfish Share definition Flag The act of diarrheating excessively into a magnum-sized condom, tying the condom, and popping it over your mate's face. Guy: Hey, babe, I'm going to give you the sloppiest Belgian Blowfish you've ever hard. Belgian Blowfish by KevinIsWin February 1, 2009 Get the Belgian Blowfish mug.