Even though they're each highly successful in their own right, it seems like Madonna and Janet Jackson are still pop rivals.

The divas were both partying it up at Butter in NYC on Monday when her Madgesty snubbed Janet, giving her the cold shoulder all night long.

And, to make things worse, Madonna was chummy chummy with pop darling Shakira (showing up "hand in hand"). Could a duet be in the works?

The Material Mom was having an into the groove good time, dancing on banquettes with Demi Moore, Ashton Kutcher and Penelope Cruz.

But Janet, who was seated, a few booths down "was not invited to join Madonna's crew," said one spywitness.

Ouch!