I am putting this here only so you recognise it, not so you use it. Wanker is a British insult for a man you think is stupid, arrogant, or unpleasant — especially someone who shows off or thinks he is important when he is not. It is strong and rude. Written down its literal meaning is about masturbating, and that is exactly why it is offensive.

Where you will meet it: British films, football crowds, comedy, online arguments. It is very common in Britain, Ireland, Australia and New Zealand, and much rarer in America, where people often know it only from British television. There is also a hand gesture that goes with it. Between close British male friends it can be almost affectionate — 'you absolute wanker' after a bad joke — but that only works inside a friendship, and a learner cannot judge that line safely.

So: understand it when you hear it, and do not say it. If someone says it to you, you are being insulted. If you need to say something similar, 'idiot' or 'jerk' will do the job without the risk. This is a word to keep behind glass — know what it is, never touch it.