This is the description of a man who behaves like a monster and who has trouble socialising with other humans. These individuals often reside in the Midlands area of England, but are also found in towns on the North West of England.
Nigel: That guy over there looks mental, he is giving me dirty looks and is making crazy noises that are quite scary.
Paul: Watch yourself, he's a "Monster Man" so I wouldn't start anything. He will rip you in two.
Nigel: I wasn't going to.