Not necessarily a put-down of the person in the argument, but a line that killed it.
My Dad had a go at me when I was at school, thought I was ‘falling in with the wrong crowd’ or some such (I wasn’t, but had been partnered with a couple of our class idiots for a project and was being more-or-less forced to hang about with them until the work was done).
Dad: “That Lee lad, he’s a bad ‘un”
Me: “Dad, Lee isn’t **** smart enough to be a bad ‘un. If he had a brain he’d be dangerous, but he hasn’t. I’ve had yoghurts worse than him…”
For once, my smartarse father had no response.