Today Cameron turned the mockery treatment on Nadine Dorries, his latest political foe. There is nothing more dangerous in politics than descending into a figure of fun.
As every politician knows, the biggest enemies are always those found in your own party. So it's no surprise that the big contest in this lunchtime's prime minister's questions was between Cameron and the Tory backbencher who had called her party leader "gutless" at the weekend.
This was Nadine Dorries, perhaps the most effective right-wing troublemaker ever to emerge from the rolling fields of Mid-Bedfordshire, who is very experienced when it comes to winding up the PM. He has been interfering in her abortion amendment, which MPs are spending the afternoon debating. It tackles the question of who provides counselling for pregnant women considering an abortion – an ethical issue which MPs are allowed to vote on with their consciences, free of a party line this way or the other. Dorries was fed up that Cameron had made clear he wouldn't back her amendment.
"He is strongly pro-choice, a male feminist, but sensible and doesn't want to see women abused," she seethed on Sunday. "I just wish he had the guts to say outright it was Clegg who forced him to U-turn." All right-wing-thinking Conservatives know who to blame when Cameron goes all liberal, that's for sure.
You have to admire her pluck. Dorries is not the sort of gal to say one thing to a national newspaper and another when in the prime minister's presence. So when Speaker John Bercow called her name in the Commons this lunchtime, she gave Cameron both barrels. "The Liberal Democrats make up eight per cent of the members of this parliament and yet they seem to be influencing our free school policies, health, many issues," she griped, over a rising tide of noise from excited MPs. They all knew her real motivation.
"Does the prime minister think it's about time he told the deputy prime minister who is the boss?"
More uproar, of course. Clegg simply chuckled to himself. Hundreds of MPs preferred a more boisterous method of communicating their enjoyment of her thoroughly uppity jibe.
Cameron looked a little redder than usual as he stood up to answer (summer holidays just over, of course). But he could sense this one required some sensitivity. "I know the honourable lady is extremely frustrated – ah – about…" Nadine 'frustrated' Dorries? That's not going to go away in a hurry. Cameron probably didn't mean any kind of innuendo, but that didn't stop the unintended joke. He knew it. The Commons knew it. Dorries, who looked like she'd been slapped around the face by a wet Labour leaflet, knew it. Did I mention the uproar?
This was a situation which the PM, who is as adept at the tact business as you'd expect for someone at the summit of the political world, could have wriggled out of. Doing so would have required effort which his brain just wasn't prepared to make. But amid the din he chose not to, riding and embracing the laughter flowing around him. "I'm going to give up on this one," he said cheekily, sitting down quickly. Laughter deep from the Commons' collective belly turned its focus purely and simply on the uncomfortable figure of Dorries.
It was a moment of distilled humiliation. Cameron's combination of mockery and dismissal, however intentional, was the worst possible precursor to her abortion debate. Every decibel of laughter lowered her political capital. As Dorries discovered, taking on the prime minister can be a bruising business.