Celeste Beard Johnson saw red when she was getting grilled behind bars ... to the point that she freaked out on interviewer David Scott.

In a clip from the upcoming season 4 finale of "Interview with a Killer," you can see her start to shake when he accuses her of living in an "alternate reality."

As David's talking, Celeste -- who's serving a life sentence over the death of her late husband, Steven Beard -- gets so mad that she hangs up and turns around ... declaring to the guard that she's done with the conversation. But it doesn't end there ...

David tries to get her back on the phone, which only seems to piss CBJ off even more. She picks back up to tell him off and accuses him of talking down to her.

She starts raising her voice, hurls a "F*** you" his way, and flips him the bird before hanging up again.

When he asks her through the glass if she's a narcissistic sociopath, she responds ... "No, you are an a**hole."

Celeste is still mic'd up after she walks off ... and you can hear her call David "dumb" and a "stupid idiot." You'll be able to see the intense interview play out when the finale airs on Sunday at 8PM ET/PT on Court TV, then it will be available on their YouTube Channel.