Uninteresting or unpleasant.
A stupid or contemptible person.
A gullible or easily-cheated person.
The face.
A criminal.
A large cup for beverages, usually having a handle and used without a saucer.
Motherfucker (usually in similes, e.g. "like a mug" or "as a mug")
To assault for the purpose of robbery.
To photograph for identification; to take a mug shot.
To exaggerate a facial expression for communicative emphasis; to make a face, to pose, as for photographs or in a performance, in an exaggerated or affected manner.
To learn or review a subject as much as possible in a short time; cram.