It's a great job description, to be the voice of a youth who is vaguely disaffected but still armed with a subscription to every cable music channel he can lay his eyes upon. It means you can amass a level of respect that places you among the last decade's highest pantheon of American rock groups alongside the likes of Foo Fighters and Red Hot Chili Peppers, but you still get to make a living tearing around a stage in silly hats as your trousers slip down around your hips.
That Green Day singer Billie Joe Armstrong, at the age of 37, is perfectly placed to relate to an arena full of original punks and wild-haired schoolkids probably accounts for much of the reverence afforded his band these days, although they've also amassed a weighty selection of hits in the 15 years since Dookie first saw them rise to prominence. Through a set which stretched to nearly two-and-a-half hours, we were never more than a couple of songs away from a bona fide international hit, and the spaces were filled by fan-favourite album tracks and songs from their most recent record, 21st Century Breakdown.
In the event, this show was part state of the nation address (to America), part punk rock cabaret. The bleached-blond, black eyelinered Armstrong continues to resemble a manga hero styled by Vivienne Westwood, and he fortunately doesn't go in for Bono-style sloganeering. Yet still, his group are responsible for one of the past decade's finest pop protest songs, "American Idiot", which began their encore here with possibly the biggest cheer of the night. This is Green Day's zenith, a calamitously noisy song with a perfect yell-along lyric, a wake-up call aimed at their average listener in suburban America, and – in this live context – a few pyrotechnic explosions to emphasise what a key part it plays in the set.
Arguably, it's their finest moment, but its magnificence shouldn't overshadow just how silly parts of the rest of the set were. In particular, the hat affair. With comedy cowboy's and wizard's headgear in place, the quartet merged "King for a Day" into a medley of quickfire covers; there was the Doors' "Break on Through", Ben E King's "Stand by Me", the Rolling Stones' "Satisfaction" and, possibly in dual tribute to their current location, Lulu's "Shout" and Travis' "Why Does It Always Rain on Me?" Although sections of the audience seemed to love this, it was sheer cabaret, the arena- rock equivalent of a respected actor pulling on a funny costume and hamming it up in panto.
That's the Green Day dichotomy, really. For a band who have grabbed the attention of so many, they still seem happy to coast along on the same gurning, jokey style they pioneered when they and a large chunk of their audience were much younger. There are flashes of maturity in the title track of the new album, and in its contemporaries "Know Your Enemy" and "21 Guns". But such enduring common-room anthems as "Basket Case" and "Brain Stew" seem strangely out of place coming from a band who might hope that their music will mature alongside them. It is, you suppose, the universal dilemma of the ageing punk.
Perhaps the most unifying moment of the set other than "American Idiot" was also its most subtle. After announcing "Jesus of Suburbia" as the last song, Armstrong then carried on with a three-song solo acoustic set, backed not by tickertape explosions and showers of sparks, but a canopy of sky-blue spotlights and the quiet attention of the crowd. These songs, including "Wake Me Up When September Ends" and the uncharacteristically tender "Good Riddance (Time of Your Life)", emphasised the folksy heart that separates Green Day from the snotty show-offs they so often pretend to be.