"Vanderpump Rules" fans should sit down in front of a fan when watching the season 12 reunion ... because Lisa Vanderpump and Andy Cohen says it's hot!

We caught up with the stars as they were leaving Lisa's restaurant Sur in West Hollywood Friday night -- right after they filmed the reunion ... and they both used the word "sexy" when describing the event.

Lisa told us the show was funny, joyful, tearful ... and pretty sexy -- later joking she was totally referring to herself when it comes to that last descriptor.

Interestingly, Cohen also used the "s" word to describe the evening ... and, he didn't say he was just talking about LVP.

As for how this new cast of 'VPR' did in year one ... Andy and Lisa gave them glowing reviews -- praising their honestly on camera and promising they'll be even better in their sophomore outing.

We also asked a few of the show's stars -- Demy Selem, Kim Suarez and Audrey Lingle -- how they felt the reunion went ... and, they were clearly exhausted -- and a little pissed -- at unnamed parties for not taking great accountability during the reunion.

They're still rolling out episodes of 'VPR' season 12, so the reunion won't come out for a while ... but sounds like it will be must-see TV when it does drop!