Playgirl Threatening Lawsuit Over Reality Star's Penis

Some photos of a celebrity man nozzle has the folks at Playgirl all hot and bothered ... after the dong shots were allegedly stolen and leaked to the Internet ... TMZ has learned.

The man connected to the wiener is "Real World: Hollywood" muscle head Joey Kovar-- who banked $20k to pose in a fully nude spread that was supposed to be revealed later this year.

So when the photos turned up on TheDirty.com recently -- Playgirl wasn't amused ... and fired off a cease and desist letter to the website. Playgirl is demanding Dirty honcho Nik Richie immediately take down the shots ... or else face the wrath of a lawsuit.

At the time of this post, TheDirty had not removed the pics ... and we're told the site has no plans to take them down.