Birdman and R.Kelly

Producer and part-time rapper Brian "Birdman" Williams is known for making hits for Lil Wayne and other members of his Cash Money arsenal but the New Orleans native sites working with singer R. Kelly as his biggest musical mistake.

In an interview with Ozone Magazine, Birdman didn't mince words when it came to a failed collaborative effort with the R&B crooner "Probably the worst investment I did was f----- with R. Kelly," he said. "That was a waste of my time. I could've made money if I wasn't f----- with that clown a-- n----."

Although plans for the album fell through Kelly went on to work with Jay-Z on the 'Best of Both Worlds' album, a move that also did not end well. Despite releasing the album, Jay and Kelly ran into trouble while on tour in 2004. During a performance at New York's Madison Square Garden, the Chicago native pulled out of the performance alleging that his life was in danger, claiming that members of Jay's entourage were waving guns at him during his set. If that wasn't bizarre enough Kelly said he was later pepper-sprayed by a member of Jay's crew backstage, which sent him to a nearby hospital.

"Ridiculous," Jay said of Kelly's claims in a later interview. "That's Madison Square Garden. You cannot get a gun in Madison Square Garden. Does he know where he's at?" Needless to say, the tour was nixed and re-named Jay-Z and Friends and included appearances by Ja Rule and Mary J. Blige.

Kelly has since stopped doing joint albums and recently announced plans to add a whopping 15 more chapters to his 'Trapped in the Closet' songs and mini-movie series.