This is a term derived from the commonly known insult 'mug'; meaning someone who has been treated like an idiot, or been severely nieve.
If you have been 'mugged off' someone has clearly made you into a 'mug', hence you have been insulted deeply. A 'mugging off' often deserves a swift backhand across the perpetrator's derriere.
'If you don't stop dissin me crew you're gonna have the ultimate muggin off in front of your pals'
'I'VE BEEN MUGGED OFF! HE DISSED ME AND ME CREW'
'You muggin me off? Nah bruv nah, i'll have to get me pals to blaze you now innit'
When someone disrespects you, and causes offence by insulting you, how you act, or your style. sometimes when your posesions are mugged off. Can result in you cutting them first if mugged off infront of ones pals. (being mugged off infront of your pals is 10 times as bad, as it makes you look like a mug)
for reference watch football factory.
"yo bruv, your wheels aint fly"
"hey jason, you failed at life"
or when your at a party and you get mugged off and then mark wont answer if hes mugging you off
Having someone masturbate you with one hand, then catching the jizz in a mug that they are holding with the other.
"I met an interesting girl/boy last night. Gave me a right good old mugging off."
or
"I was down at WhateverBar this weekend. The number of people who were looking to get mugged off was surprisingly low" / "Really? There must be a mug shortage in town".
or
"Had a disappointing evening. Got mugged off with a flimsy plastic cup." / "Well, ceramics is a dying art."
It is said of the situation where a person has the bad luck to make contact with his testicles against an undefined surface or object, intentioned or not.
Given the nature of the word, it is more appropriate to design cases where the interaction is made with a moving object, for example, a ball.
Although it is extremely painful for the victim, it tends to be considerably funny to people who witness it.
Today in the baseball game the pitcher took a nutshot; the baseball hit him in the nuts.
Man, I just watched the funniest nutshot video ever.