Classic British insult for someone you reckon is an idiot, selfish, or just acting like a total pillock. It can be light banter between mates or proper venom when someone’s done you dirty. Technically it means a masturbator, but day to day it’s more about vibes than biology. Honestly, ridiculously useful in London.
"Some wanker in a white van cut me up on the North Circular, then had the nerve to beep like I’d nicked his Nando’s. Absolute wanker, mate"