A ghetto balaclava or ski mask. Usually a hat with eye holes. Sometimes just cloth crudely stitched together.
Its often used in robberies as its cheap and disposable. Some robbers are also too poor to afford a real ski mask and so must use a mugger mask.
Can also refer to a balaclava or ski mask.
Fat albert is wearing a mugger mask.
The cops threw Johny off his bike because he was wearing a mugger mask and carrying a knife.