So, what does the singer do while the Guitarist (or other) sings 'his' song?

So, discounting those lead singers that 'carry on playing guitar' e.g Joe Strummer...

Do they all leave the stage for a cig/drink (LiamG/RogD) ?

Jim Reid has a sit down, or does the Tambourine bit..

backing vocals on the chorus

"this is the real motherfuckin deal y'all"

Tambourine or gtf.

What does Mick do when Keith sings lead?

Answering my own question, it seems he goes offstage (per youtubes of recent "Little T&A" outings).

the guy standing and clapping to the left of the frame is the lead singer of ram jam

https://www.youtube.com/watch?v=I_2D8Eo15wE

the song is actually performed by the guitarist's previous band starstruck, none of the others in the video feature on the record

Nick Cave took on guitar while Rowland sang Shivers at least part of the time.

prance around twirling things?
https://www.youtube.com/watch?v=_LeDp3jv9Bk

What does Mick do when Keith sings lead?

― bored by endless ecstasy (anagram), Tuesday, June 4, 2024 9:08 AM (four hours ago) bookmarkflaglink

Answering my own question, it seems he goes offstage (per youtubes of recent "Little T&A" outings).

― bored by endless ecstasy (anagram), Tuesday, June 4, 2024 9:12 AM (four hours ago) bookmarkflaglink

Apparently there was a formal clause introduced for the Steel Wheels tour that Mick would leave the stage during Keith's songs, hence the end of sharing the mic for 'Happy' and whatnot

backing vocals on the chorus

One of my favorite things is when a lead singer does this to "support" a weaker-voiced instrumentalist but starts very, very obviously throwing on lots of competitive sauce or volume to seize attention and prove how much better they are

take a slash or a crap

When Captain Beefheart did that one tour in Frank Zappa's band apparently he'd sit at the side of the stage sketching the other members of the band... including Frank... with horns.

... I mean, Frank with horns, not the other guys in the band, he liked them.

drugs

your mom