The colloquial British-English noun Glasgow kiss denotes a headbutt.

This noun alludes to the reputation for violence accorded to some parts of Glasgow, a city in west-central Scotland.

The noun Glasgow kiss occurs, for example, in the following from the Evening Standard (London, England) of Tuesday 9^th July 2019:

Kirsty’s unfortunate Glasgow kiss

NEWSNIGHT presenter Kirsty Wark is planning corrective surgery as her nose “has been broken for 27 years” and she can “only breathe out of one nostril”. “I was head-butted by my son when he was two,” Wark tells the Fortunately podcast. As it was during an Old Firm Celtic v Rangers derby, there was “no chance of going to A&E in Glasgow”. Wark went to a specialist a few days later, where she was fitted with a “metal thing”. But the device failed to repair the damage and now she is planning a nose job.

The earliest occurrences of the noun Glasgow kiss that I have found are as follows, in chronological order:

1-: From the Daily Mirror (London, England) of Wednesday 2^nd June 1982:

Glasgow forgets its anger to pay tribute to John Paul
The Pope sparkles in the city of broken glass
Paul Callan

Glasgow has its own way of welcoming people. All too often—particularly if it is near closing time—there is a broken bottle gripped in the fist of greeting.
Or there’s the Glasgow Kiss—a sharp whack on the nose with the forehead.
But it was different in Glasgow yesterday. In this city of broken glass, where a casual greeting can sound like a threat, they put away their traditional anger, doused their fighting spirit and paid tribute to Pope John Paul.

2-: From the television column Did you watch…?, by May Jeffrey, published in the Evening Post (Nottingham, Nottinghamshire, England) of Tuesday 30^th October 1984:

Robbie Coltrane […]’s one of the survivors of A Kick Up The Eighties who is back on BBC-2 with more “alternative comedy” in Laugh? I Nearly Paid My Licence Fee.
Unfortunately, the title, and title song, were among the funniest parts of the show.
But as Robbie’s a tough-looking bloke, not afraid to give a horse a “Glasgow kiss” in last night’s show, and as he did devise a superb sketch about a bigoted Orangeman, I’m not about to stick my neck out without first watching the show again next week.

3-: From the column ‘On the lighter side’, by Ray Bryant, published in the Reading Evening Post (Reading, Berkshire, England) of Friday 4^th January 1985:

Royals in new family bust-up

A NEW family row has split the royal household, I can confidently reveal today.
According to a safely uncheckable source, it is the most serious rift yet in the regal ranks.
Prince Harry, I am told, is no longer talking to Prince William.
He hadn’t been saying much anyway, being only three months old, but now the break is complete.
Prince William is reported to have snatched away a train that little Harry had for Christmas.
That would not have been so bad, except that it was the Advanced Passenger Train presented to the royal babe by British Rail. who haven’t got the room to play with it themselves.
An angry Prince Harry then belted his big brother across the shins with a jewel-encrusted rattle.
Wills gave Harry a swift kick in the monogrammed diaper. As the fight developed dangerously, Zara Phillips rushed in to break up the pair.
She was head-butted by her brother Peter, who had been training his little cousins in karate and wanted to see how they’d do.
“Have a Glasgow kiss, sis, and keep your nose out of it,” he snarled.
Peter in turn got a cuff around the ear from Princess Di, with a book on child psychology given to her—ironically—by Princess Anne.