TMZ Live: Katy Perry & Riff Raff -- Post-Hookup Bragging

Katy Perry's rebound after John Mayer -- Riff Raff?!!? Strange as it sounds ... we got the rapper talking all about his night with Katy -- but who brags about hooking up with one chick WHILE there's a different chick grinding on your crotch? Riff Raff, of course.

Plus, Gwyneth Paltrow and Chris Martin's split has definitely been a long time coming -- and we have the proof in a real estate deal gone wrong. Did Gwyn shut down Chris' plan to move out a year ago?

And, Charlie Sheen joins us -- he's mounting a full offensive against John Mayer over the singer's watch lawsuit ... and it gets nasty.