Barry: ' Damn i lost your money! '
Gazza: ' Ah you mug!'
Can be used as an insult but is commonly known to be used to call friends as a joke.
Ah Gazza is a MUG
what the hell you mug.
jog on you mug.
Nathan: -walks in-
Caity: I'll text it to you later, I can't say it in front of this mug.
Briitany: Sorry about not calling you back last night, I fell asleep.
Caity: Don't talk to me, you mug. jk.
Its hard to give a precise definition, but basically a mug is a naive or easily cheated person, an idiot, or just somebody you dont like
Me: "You mug!"