Vulgar British slang meaning to masturbate. The phrase is blunt and casual, used mostly among friends in humorous or candid contexts rather than formal ones. It's part of a long tradition of British slang that treats bodily acts with matter-of-fact irreverence. Common enough that it appears in comedy, TV, and everyday lad banter without causing much shock.
He'd been alone in the flat all afternoon, which his flatmates assumed meant he'd knocked one out and watched three episodes of something terrible.
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(slang, vulgar) To masturbate.
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Regional slang from around the English-speaking world — British, Australian, Irish, Caribbean, Nigerian, Filipino, AAVE, and the hyphenated-English dialects that make the internet sound local.
See all Regional & Other slang on Slangora.