noun

• (slang, often derogatory) The face.
  "[…] 'let him go, I tell you, or I'll be after breaking your ugly mug,' and with that I gave him a dig that knocked him into smithereens."
• (slang, derogatory) A gullible or easily cheated person.
  "He's a gullible mug – he believed her again."
• (UK, Ireland, Australia, New Zealand, Singapore, Hong Kong, derogatory, slang) A stupid or contemptible person.
• (slang) A criminal.

verb

• (transitive, obsolete, UK, Ireland) To strike in the face.
  "Madgbury showed game, drove Abbot in a corner, but got well Mugg'd."
• (transitive) To assault for the purpose of robbery.
• (intransitive) 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.
  "The children weren't interested in sitting still for a serious photo; they mugged for the camera."
• (transitive) To photograph for identification; to take a mug shot of.
  "Perhaps if I told you that there were forty arrests made in one day here, you will realize that with this small equipment available in the Sheriff's Office, it is very difficult to get mugs. These people are being mugged as they are being arrested but with an entirely inadequate force at work prints have not as yet been made."

adj

• (archaic) Easily fooled, gullible.
  ""Great heavens! Is it?" Drummond helped himself to marmalade. "And to think that I once pictured myself skewering Huns with it. Do you think anybody would be mug enough to buy it, James?""
• (Bermuda, slang) Uninteresting or unpleasant.
  "But anyways, I stayed back a second year and my papa was visiting when momma was opening de report card. Papa gave me de muggest moment in my life like."

noun

• (slang, African-American Vernacular) Motherfucker (usually in similes, e.g. "like a mug" or "as a mug")