The severed head is an improvised weapon seen occasionally in the Madness Combat series. In the episodes, the severed head is the head of an enemy Hank decapitated. On several occurrences, Hank used severed heads to bludgeon his enemies, sometimes to death.
The decompiled version of Madness: Project Nexus has the data for a severed head as a melee weapon. Like the urinal, it is not a weapon that can be legitimately used in the game.