look up any word, like sex:
 
1.
ok so here we go, this was first coigned by a british urban group with a twist called 'the streets' when it became the title of possibly the best song on their first album 'original pirate material'. Essentially the phrase means 'dont shoot yourself in the foot by getting obsessed with a girl who isnt worth it.' - dont be a mug, quite simply, GET A GRIP!
the corus from the streets' song:

"Hold it down boy, your head's getting blurred
I know you cant stop thinking of her
By all means you can vibe with this girl
But just don't mug yourself, thats all don't mug yourself. "
by Matt_uk August 15, 2006
 
2.
Noun
1. Brit., informal for being stupid or gullible about what a person is telling you.

2. U.S., Losing your identity in a co-dependent relationship.
1. She's so full of bullshit mate.

No no its not like that, I can trust her.

Mate, "Don't mug yourself"

2. She says she likes artsy guys.

Do you think your an artsy guy?

I like art; Yeah I could be an artsy guy I guess.

Ugh, Don't mug yourself.
by Zombilly July 25, 2010
 
3.
don't screw yourself over mug yourself
She has STD's dude don't mug yourself
by L'pool doggy February 27, 2005