What it means
A very British little insult for someone being daft, clueless, or just mildly irritating. It's not heavy-duty abuse, more the sort of thing you lob at a mate who's done something stupid again, or at a stranger who's acting like a total knobhead in a low-stakes way. More eye-roll than war declaration.
Usage examples
"Some prat wedged himself in the Tube doors with a massive suitcase, then acted shocked when everyone started tutting and squeezing past."
"Don't be such a prat, you've put the batteries in the wrong way round again."
"Look at this prat trying to pay for the bus with an old library card."
"He's not dangerous, just a prat who thought setting off fireworks in the rain was a solid plan."
"You absolute prat, you've been pushing the pull door for a full minute."
Where it comes from
It goes back to old British thieves' cant, where prat meant the buttocks. Later it slid from naming your arse to calling someone a fool, which is a pretty classic insult migration if language is feeling cheeky. That's why it has that faint backside-family whiff, even though now it sounds fairly mild.
Other ways to say it
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