If they didn't like it/didn't think it was good enough, Stand up comedy would not be on the album. Thus, it can't be the reason why SUC doesn't get played live.
They even had a T-shirt in tour merchandise with the "stand up to rock stars" line.
I don't mean to be the 4th person to object (piling on) but it must be said...
Have you ever done anything creative like paint a picture, write a poem, make a short film, write a song or write a short story, etc.?
If you have, then you absolutely would know the feeling of seeing something that
you yourself did, perhaps minutes, hours, days, weeks, months, years later and said "my God that is shitty!"
When you are creating, you are caught up in the feeling of creating.
You are too clouded to be objective about the creation.
This PRECISELY why long studio session will doom most any album.
This was the same argument made around 2004 about song selection (Native Son vs Vertigo, Xanax vs Fast Cars, ABOY alt vs ABOY htdaab, etc.).
If U2 put it on there, then it 'must' have been better...uh,
no.
However, with all that said - it must be said, that at the time they delivered that album to the label (I would say around the first of Dec, end of Nov in 2008) that they did think it was good enough.
Just like they were comfortable with all those Chris Thomas versions for about a year before dumping them and rebooting. SUC< I would guess (can't recall) was one of the late comers in the 'delay', along with Crazy Tonight. It was called For Your Love, that much I do remember. and my gut feeling is, a better lyrical take would save that song a lot of the grief it receives.
P.S.
The reason it wasn't played live - IMO - was because they knew they made a mistake a few months (if not earlier) after they handed that album over to the label. By then, it was too late.