The singer was back to bantering with the crowd Monday, only this time she wasn't talking subs ... she was going on about "Vanderpump Rules." Specifically, Adele wanted to know who the guy that cheated was ... and what exactly he does for a living.

It's a fair Q. Folks who don't watch the show -- but who might've heard about the drama regardless -- have probably been asking the same thing ... and Adele got some answers from ticket holders. Well, sorta ... people weren't all that helpful in painting a clear picture.

Adele polled one fella in the audience, and he simply blurted out ... "He's trash." She jokingly agreed, but clearly wanted her question answered -- and he told her Tom's a server who's trying to be a singer now. That's not *entirely* accurate ... but Adele seemed satisfied.

For those unfamiliar ... Tom is a local restaurant/business owner in L.A. who mingles with the 'Vanderpump' staff as a bartender. He's been part of the cast since pretty much the beginning, and yes -- he is indeed in a band ... and he does, in fact, sing.

While Adele didn't seem privy to any of that info ... she's certainly heard about him pulling a fast one on his longtime girlfriend, Ariana Madix, by hooking up with her best friend and fellow castmate, Raquel Leviss -- which blew up in his face earlier this year after we broke the news on the affair.

As we've reported ... there's been a lot of mud-slinging in the aftermath, but now -- Bravo's ready to do it all over again. Only problem is they haven't signed Raquel for the new season just yet ... as she remains at her mental health facility ... and they're starting production on Wednesday. Obviously, they want her back.

Time will tell if she inks a deal ... but it'll also be interesting to see if the 'Scandoval' has actual legs. This thing's starting to feel fully squeezed -- and there might be some fatigue.