The 'Vanderpump' panel is underway in Vegas Friday as part of the weekend-long convention -- and as we all expected ... the dude walked out onstage to a chorus of boos from the audience, although it sounds like it might've been more fun booing ... if that's even a thing.

Anyway, Tom took it in stride and powered through his questions ... despite the fact that some continued to playfully hiss and jeer as he talked. He's a villain -- and he owns it.

Now, in terms of seating arrangement -- sources on the ground tell TMZ TS and his ex, Ariana Madix, weren't really anywhere near each other while they were up there ... however, we're told that wasn't necessarily done as a result of any sort of request from either of 'em.

In other words ... the higher-ups at Bravo appear to have just plopped the two of them where they ended up by mere chance, probably assuming there's still bad blood over the cheating.

There's certainly unfinished business between AM and Tom -- which was previewed in a sneak peek at Season 11 ... showing Ariana freaking out at somebody, who many have presumed to be Tom. In one particular moment in the trailer, she says ... "Ruin my life, my home, and then fucking attempt to kill my fucking dog. My lawyer will be dealing with you!"

On its face, it would seem she's talking to Tom here ... but time will tell if that's true.

Anyway ... during the Q&A panel, our sources tell us Lala went to bat for him in front of everyone -- telling the crowd they oughta have some respect for Tom considering he showed up, and continues to put himself out there with his band despite the backlash.

Of course, what's interesting about that lies in what Lala was saying about Tom earlier this year -- including during the reunion, where she was one of the fiercest ones dragging him.

We also got her on camera around that same time ... and there, she called Tom a narcissist.

Now, however, she seems to have changed her tune -- and appears to kinda be in his corner here. The two of them have been tight on the show for years now, so perhaps all the outrage fatigue finally kicked in on her end ... as it has for so many others as well.