Acid-tongued JOAN RIVERS hates OPRAH WINFREY and wants the world to know it!

The plastic surgery poster girl puts the corpulent chatty at the top of her enemies list.

"Joan says Oprah is the biggest phony in the world," a close pal told The ENQUIRER. "She makes Joan sick.

"She wishes Kitty Kelley had called her when she was penning her tell-all book about Oprah because she would have dished unmercifully."

Promo-ing a new Joan doc, Rivers slammed the Big O some more: "Oprah’s just very cold. Oprah – if she don’t need you, she don’t know you!"

And the vet entertainer told her pal: "People think Oprah exudes all this caring. Well, have a closer look. The only thing she cares about is Oprah!"

The plastique enhanced comic believes the talk-show titan "is completely opportunistic," according to the pal.

"She feels Oprah’s real gift is exploiting people’s suffering and emotions and turning them into TV ratings."

Rivers also complained to her pal that no one knows "the real Oprah. Is she gay? Is she straight? No one’s really answered that yet, not even Kitty Kelley.

"Oprah’s always trying to hide, but it’s hard when you’re that fat!"