The bitchfight on this week's episode of "Vanderpump Rules" was not just reality TV BS ... we've learned one of the stars ran to the cops afterward ... fingering her castmate.
Stassi Schroeder accuses Kristen Doute of sleeping with her ex-boyfriend ... calling her a "dirty f**king whore" ... then hauling off and smacking Kristen in the face. She also douses Kristen with a drink -- while the rest of the cast looks on.
The fight was not scripted ... and Kristen was so enraged she was gunning to get Stassi prosecuted and filed a police report.
But we found out the criminal case hit a dead end ... cops needed a follow-up interview but Kristen was uncooperative.
Lisa Vanderpump -- who employs both Stassi and Kristen at her restaurant -- tells TMZ the women have since made up telling us, "I know that Stassi was very sorry and regretted it. I made Stassi apologize to Kristen and hope that they could move forward."
Now everyone can be their bitchy selves again.