Mug

n.
  1. A kind of ceramic or metal drinking cup, with a handle, -- usually cylindrical and without a lip.
  2. The face or mouth; as, I don't want to see your ugly mug again; -- often used contemptuously.

v. t.
  1. To take property from (a person) in a public place by threatening or committing violence on the person who is robbed; to rob, especially to rob by use of a weapon such as a knife or gun.

To rob a person or a business indoors is not usually referred to as to mug, but to stick up or hold up.