But it was part of a trend. Last week, Rishi Sunak dubbed his Labour opponent "Sir Softie". Which without the context - an attack on Sir Keir's crime-busting credentials - sounds like a not-very-threatening ice cream man.

Both men have got a lot of work to do on their nickname game, according to author and political commentator Andrew Gimson.

"They are both quite professional. Neither of them are natural name callers and that is one reason why it doesn't come out with any conviction."

Boris Johnson was better at it, he says. The former prime minister liked to taunt Sir Keir as "Captain Hindsight", which later evolved, if that's the right word, into the more ornate Captain Crasheroonie Snoozefest.

Many will argue that puerile name calling and personal abuse have no place in politics. They will point to Donald Trump, who built an entire political brand on nicknames and insults ("Trump was good at it," notes Andrew Gimson).

But, argues author and former Labour adviser Ayesha Hazarika, we should not be too squeamish or high-minded about political insults.

When they are done well, they can be a powerful way of distilling, or "framing", a complicated and nuanced message - a useful "shortcut" to the public's brain, with the added advantage of making your opponent look ridiculous, she says.

But she adds: "They only work if they are snappy, memorable and have a ring of truth."

There is a long tradition of insults in British politics.

Older readers may remember Labour bruiser Denis Healey describing an attack by a mild-mannered Tory opponent as like being "savaged by a dead sheep".

Then there was equally mild-mannered Sir Vince Cable getting big laughs at Gordon Brown's expense with this line: "The House has noticed the prime minister's remarkable transformation in the past few weeks - from Stalin to Mr Bean."

More recently, nicknames - which can easily be turned into social media hashtags and memes - have been all the rage, as opposed to more elegantly phrased takedowns.

Suella Braverman was dubbed "Leaky Sue" by Lib Dem leader Sir Ed Davey. Tory co-chairman Lee Anderson got the nickname "30p Lee" on social media after making controversial comments about food banks. And so it goes on.

Rishi Sunak cribbed "Sir Softie" from a headline in The Sun and it got a bit of pick up on Tory social media.

Ayesha Hazarika - who in a former life spent time dreaming up jibes as part of the team preparing then Labour leader Ed Miliband for PMQs - does not think it will catch on.

"I cannot tell you how ridiculous that was. It is so childish, it's the kind of stuff your toddler would say to you. It wasn't clever and it wasn't sharp."

But she adds: "I think both sides are really struggling with it at the moment. You have got to be prepared to be quite rude, which is fine, but it's also got to work."

Social media consultant Matt Navarra says there is "nothing new" about politicians using "divisive" language to generate social media attention, particularly on Twitter.

But, he warns, the mood may be changing. Government ministers, who are currently passing legislation to clamp down on online abuse, should be particularly careful in their use of language, or risk becoming a target themselves.

"It only takes one wrong turn of phrase, or for people to misconstrue what you have said," warns Mr Navarra, who would no doubt be dubbed Captain Cautious, if he was a member of the House of Commons.