It appears that Vanessa Minnillo might need to re-evaluate her definition of fidelity.

Despite endless reports of trouble in her relationship with crooner Nick Lachey, the longtime lovers have consistently denied that there are problems. But that certainly hasn’t stopped Vanessa from acting very single lately.

The former MTV hostess reportedly showed up alone at Prive in Las Vegas recently to celebrate her friend Malin Ackerman’s 31st birthday. She proceeded to have a few Grey Goose vodka drinks and trouble ensued.

Page Six has the rest of the story:

Then she plunked herself on an unidentified man’s lap for “a while,” before challenging a Michael Jackson impersonator to a “Thriller” dance-off atop a dancing platform. Our spy says, “She matched him move for move, complete with a lick of her palm, grab of her crotch and other non-PG-rated moves. She even completed her dance by kicking off her shoes and climbing off the platform in drunken prom girl style.”

This is certainly not the first time Vanessa has been caught “lap dancing.” Just last month she was getting way too close to 90210 actor Matt Lanter. While partying at SLS hotel in L.A., “she sat on Matt’s lap and really close to him for two hours at the party.”