What exactly does it mean to "mug somebody off" in British English?
I tried looking this up at the Urban Dictionary, but it gave only one net-upvoted definition, and that definition wasn't even clear. The background for my question is coming my watching from a movie with lots of Cockney English sounding speakers; somebody says something to another a bar, and the person being spoken looks upset and yells back, "are you trying to mug me off?"
What does it mean?
I'm British and I do recognise the phrase, and you are correct it is usually used by Cockneys.
Here is a reference to the reality TV show The Only Way is Essex where someone feels that they have been made of fool (mug) of by his date, who is dancing with another man. She responds that she didn't make him look like a fool (she didn't mug him off).
In The Streets song 'Don't mug yourself' released in 2002, advice is given to a friend not to mug themselves over a girl (not to make a fool of themselves over a girl).
To be mugged off means that you are being made a fool of by someone taking advantage of you. There are two different meaning to the word mug that comes into context with you use this phrase.
to mug someone, is take something from someone by use of force. So in this context taking someone of their respect/street cred.
to be a mug, is to be fooled by someone, or to be taken advantage of.
From rhyming slang. Mug and spoon (i.e. what you need to drink soup) — loon. Thus lunatic. Thus be maddened or made mad.