Jay-Z and R. Kelly, don't try this again.

Once upon a time, there was The Best of Both Worlds, a record our beloved Young Hov and our dirty old Kels (as he likes to be called, apparently) recorded and released right around the peak of Kelly's legal troubles.

Spooked by the controversy, Jay refused to do any promotion for the album, and it tanked. But, defying all logic, the two incompatible superstars decided to try it all over again with Unfinished Business.

Bad idea.

It's not that Jay-Z and R. Kelly couldn't make a good rap/R&B collaboration album, but it's not gonna be together.

It's very clear, even on a phoned-in record like Unfinished Business, that R. Kelly doesn't deserve to be in the same room as Jay, and Jay seems like he'd probably be OK with that.

In fact, the two are so completely incompatible that their recent tour fell apart when the two stars stopped speaking and (get this) somebody in Jay's entourage sprayed R. Kelly in the eye with pepper spray. The new Lennon and McCartney, these two ain't.

It's Kelly, not Jay (who sounds bored, but at least competent) who turns the album from an unfunny joke to a total embarrassment.

I'm not sure which of Kelly's bad lines is my favorite: "Sex was so good, we have to do the remix," or, for no real discernible reason, blurting out, "I think I just saw a dolphin."

Either way, he's a complete joke and manages to stomp all over the good name of not only Jay but top-tier guests Memphis Bleek, Slick Rick and Doug E. Fresh.

So why does R. Kelly insist on screwing up other people's careers with his bad singing?

Well, to borrow a line, that's our Robert: always peeing on people.

-- By Paul Thompson