The few times it’s happened I’ll do the intro to Joplin’s Summerime”. If I’m sorta feeling it I’ll continue while trying to get someone to sing. If I’m not feeling it I’ll hand the guitar back and admit my hands hurt and thank them for the opportunity
No reason to be rude
Me and my wife were in an underground club in Prague once and they were passing around an acoustic guitar. My wife said "if it comes to me I'll play What Can You do with a Drunken Sailor," but the guy right before her played it.
I never go to parties, so this is purely hypothetical. Despite that, I’m the kind of guy who likes to be prepared “just in case” so I have two such songs at the ready: Michael Penn’s “No Myth” and Joe Jackson’s “Is She Really Going Out With Him?”
I somehow have Don't Think Twice It's All Right and Just Like Tom Thumb's Blues fully memorized with a nice little solo. I think I also know a couple of Mississippi John Hurt tunes to the same level, I can bang that stuff out anytime.