Randy Jackson Bitches About Paris -- Debbie Rowe PISSED

Randy Jackson is pissed that his niece, Paris Jackson, is confined in what he believes is a psychiatric hospital and thinks something really stinks ... but Paris' mom thinks he's delusional.

Randy just tweeted, "I just hate the fact that you [Paris] will probably still be there on my brother's birthday." Randy adds, "She is not psychotic. There is no reason for her to be in a psychiatric hospital this long away from her family."

But we've learned Debbie Rowe, Paris' mom, is livid at Randy and is telling friends that he doesn't know what he's talking about. We're told Rowe said, "As usual, he's grossly misinformed. He doesn't know what he's talking about. He has no idea where she is. She's not in a psychiatric hospital."

Rowe is saying Randy is just bitter because no one wants him to testify in Michael Jackson's wrongful death trial because he's irrelevant.