What it means
When you slag someone off, you're having a proper moan about them behind their back or straight to their face — it's that deliciously bitter art of tearing someone down with words, whether they deserve it or not. The phrase feels like the verbal equivalent of chucking a pint over someone's reputation, and it's the go-to move when the gossip hunger strikes and you just have to chew on someone's character for a bit.
Usage examples
"I heard them slagging off the new manager in the break room, going on about his daft haircut and all."
"Don't just slag me off to your mates — if you've got something to say, come say it to my face."
"They spent the whole dinner slagging off her ex, and honestly, it was the best entertainment we'd had in weeks."
Voice comments
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Where it comes from
Slag off comes from the old mining word 'slag' — the stony waste stuff left after smelting metal, basically worthless rubbish. So when you slag someone off, you're metaphorically reducing them to that same low-grade muck. It started creeping into British slang in the mid-20th century, probably bubbling up from northern industrial towns where mining and metalwork were the backdrop of daily life, and it's been rolling off tongues ever since.
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