Politics can be rough and we expect our politicians to have thick skins.

But we also expect our prime minister to behave like a prime minister - to rise above the jeering and the finger pointing and treat people with the respect we like to believe he commands from others.

David Cameron is an impressive performer in the House of Commons, demonstrating supreme confidence and usually getting the better of his opponent, Labour leader Ed Miliband.

Sometimes, though, he comes across as the public school bully his opponents like to paint him as.

There was the time he told a female Labour shadow minister to “calm down dear”. Then he called veteran Labour left-winger Dennis Skinner a “dinosaur”, jesting that the Cameron children might enjoy seeing the old monster in action.

Now he’s had a dig at Birmingham MP Liam Byrne for being bald, albeit repeating a joke already used in a newspaper.

Of course, Mr Byrne can take it. So can Labour’s Angela Eagle, and Mr Skinner gives as good as he gets.

A joke’s a joke but, over time, hearing these comments from the Prime Minister stops being funny.

A backbencher could get away with it, but don’t we expect better from Mr Cameron?