Debbie Rowe -- HaHaHaHa ... I'm Not Engaged

We just got off the phone with Debbie Rowe ... who stopped laughing long enough to tell us the story out that she's engaged is "ridiculous and not true."

E! just ran a story saying Rowe is engaged to former Michael Jackson confidante/former gay porn producer Marc Schaffel, noting the big ring on her finger.

Rowe -- who was married to Michael Jackson -- tells us they're "just friends" and have been friends for years but they are "absolutely, positively not engaged."