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. "