Has there ever been one of those "who wants to play the drums?" moments in a concert where the guy just trainwrecks?

All gigs should be like that. Why aren't all gigs like that

-I remember seeing Common once, and he had a segment where he'd pull someone up from the crowd to freestyle with him. He brought up a little kid who was incredible, but I'm sure it must have backfired sometimes (although it's a good idea to choose a kid, because it's cute even if they choke).

-the famous Lars-less Metallica gig is also the opposite of this, where everyone got to live out the thought experiment of 'what if Metallica had a different drummer?'. Would have been amazing if Dave Lombardo had done the whole show.

-I have seen wack horn players sit in with New Orleans brass band countless times, but they generally can't do too much damage since there are enough people covering the parts for real.

feel like the next step is for Metallica to have a Metallica-less gig

four random dudes show up at show time and start playing, at various skill levels

That's arguably a description of the first Last Exit show.

...although they weren't playing Metallica songs.

-I remember seeing Common once, and he had a segment where he'd pull someone up from the crowd to freestyle with him. He brought up a little kid who was incredible, but I'm sure it must have backfired sometimes (although it's a good idea to choose a kid, because it's cute even if they choke).

i saw ghostface do a lazier version of this like 15 years ago, where he just invited people from the crowd to come up and rap on their own while he sat out, he may even have gone offstage. every one was terrible and it was like 20 minutes of his 45-minute set, felt like a ripoff.