For a band of Green Day’s stature, European cities detailed on the tour schedule must blur into each other after a while. However, a few songs into this set — midway through the Californian trio’s European tour — the group’s panda-eyed singer Billie Joe Armstrong revealed that he had good reason to hold Copenhagen close to his heart. “In 1991, the first time we played Denmark, people were having sex at the side of stage.” Even from a distance it wasn’t difficult to discern the approving smile. He may be approaching 40, but it seems apparent that Armstrong may never come to terms with the novelty of getting to live out his teenage dreams on a nightly basis.

At other points, though, it was a trait as exasperating as it was admirable. As he and his group hammered out 21st Century Breakdown, the powerpunk state-of-the-nation address that heads up their album of the same name, Armstrong started the first of several Freddie Mercury-style call-and-response vocal exercises. A sense that these detours are a regular occurrence was borne out by the ease with which the bassist Mike Dirnt and drummer Tré Cool kept the music ticking over while Armstrong worked the crowd.

For East Jesus Nowhere, the singer pulled up a Danish fan and asked his name. Realising that he had hurtled into a pronunciation cul-de-sac, Armstrong declared: “Well, I’m gonna call you Chuck.” From a group who have ridden back into commercial contention by writing catchy punk tunes about America’s cultural ignorance, the sight of Armstrong getting the crowd to shout “Chuck!” repeatedly was, to put it mildly, uncomfortable.

Admittedly, firing T-shirts out from a gun before Brain Stew was a nice touch, but as the off-piste meanderings got longer, their motivation started to seem more like ego-gratification than entertainment. Donning an array of wacky headgear for King for a Day, from 1997, they padded out the song with bursts of Satisfaction, I’ll Be There and — with a saxophone burst that propelled them perilously close to the Benny Hill theme — a version of Lulu’s Shout.

And so what started as a rock concert effectively ended as mass karaoke. In his encore before a dystopian backdrop of piled-high TV screens, Armstrong made no attempt to sing much of the band’s signature hit American Idiot. As his fingers automatically played the chords, he gazed on with the air of a man who had won a competition to be the singer in Green Day. Yes, it was sweet, but part of you rather felt like exhorting him to get over it.

The UK leg of Green Day’s tour begins on Oct 19 at SECC, Glasgow (www.greenday.com)

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