Definition of "mug"
mug1
/mʌɡ/
verb
third-person singular simple present mugs, present participle mugging, simple past and past participle mugged
(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.
(transitive) To photograph for identification; to take a mug shot.
adjective
comparative mugger, superlative muggest
(Bermuda, slang) Uninteresting or unpleasant.