Adam Lambert turns 31 today -- but the celebrations started over the weekend ... when he got a lap dance from David Arquette!

The "Scream" star stripped down to his briefs for the "American Idol" alum on Saturday night inside his Hollywood club Bootsy Bellows

Adam's boyfriend, Sauli Koskinen, was nearby as David showed off his moves to the packed house.

"Yup... this happened," is all Lambert said about the wild bash, though a couple photos surfaced on Twitter.

Looks like a good time, right?

Happy Birthday Adam!