Not sure if this is earth shattering, but Mew played their entire set backwards.
They came on stage, said "Thank you..goodnight", did their encore track, went off, came back on and worked through the set in reverse.

I saw Squeeze supporting The Tubes in Brighton in 1979. During the set Gilson went after a member of the audience or, possibly, a roadie, charging across the stage after the guy. Jools turned his head, looking less than surprised, but none of the band missed a beat or made any reference to it during the rest of the set. Gilson returned to his kit for the next song and they carried on regardless.

James Ray sang on The Sisterhood recording of Giving Ground, he was in the audience at the Glasgow Gig 2006, the tour The Sisters Of Mercy resurrected it. A mighty struggle between Ray and his crew, trying to get onstage ensued with them being ejected and Mr. E and his sidekicks playing on.

quite amusing - it would have been far more enjoyable if Ray had made it to the stage

I was at a Bryan Ferry concert in Auckland. Ferry had two lead guitarists, Chris Spedding and Mick Green. Halfway through the set and having just played a ferocious solo, Green - a big man - fell to the ground like a tall tree.

At first I think many people thought it was a joke after the fiery solo. Then, after he'd been lying on his back, guitar still strapped on, for a few more seconds, the crew came on and dragged him into the wings...all the while Ferry and band continued playing.

It turns out Mick had a heart attack and, I believe, is still with us. But for all we, and Ferry, knew at the time he might have died on stage, Tommy Cooper-style. Ferry didn't acknowledge it after the song and no mention was made of it afterwards. Strange.

At the recent Spizzenergi 30th anniversary show in London's 100 Club, there was a dwarf stage invasion, which is not something you see every day.

The bloke in question had been a bit loud and lairy all night but got on the stage and started wandering around. The band didn't quite know if was OK to kick a dwarf or not, but when he started to interfere with the drum kit a couple of bouncers came on and carried him off. The bloke was only about three foot tall but it still took two brick outhouse-sized bouncers to remove him.

On a less violent note. I saw Crowded House at the Hammersmith Odeon and they were taking requests at one point. One bloke thought he would be clever and requested a song that the band had made up on the spot on MTV's Most Wanted (remember that? Whatever happened to Ray Cokes?) and had only ever played once.

Fair play though - the band did manage to remember it and play it.

or Glenn Tilbrook's anyway.

As I was saying two years ago, I saw Squeeze in 1979 with Mingo Lewis on drums (see the OP above).

I went to see them again at the Greenwich Summer Concerts last month and as we wandered around during the opening act, Glenn Tilbrook was stood having a chat with some people. My brother said, 'you should go and ask him about that gig supporting The Tubes'. So I did.

Glenn remembered the gig well. I told him it was spellbinding from where I was standing. What was it like for him? "Fucking amazing. I wish I had a recording of it," were his words.

As you were, I thought I would just add that post-script.