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.
'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'
for reference watch football factory.
"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