Full House fans hoping Aunt Becky and Uncle Jesse hooked up IRL got excited when John Stamos dished about a makeout session aboard a roller coaster with his on-screen squeeze Lori Loughlin. But the 59-year-old adamantly denied locking lips with John, 60. “He likes to tell some crazy story about how we made out on the Matterhorn, and I’m like, ‘What?!’” Lori told the “How Rude, Tanneritos!” podcast in April.

While she seemed to laugh off the fib, sources exclusively tell In Touch the actress is actually fuming.

“Lori is upset that John’s put her in this position,” says a source. “It’s left her feeling like she was used for a punchline.” The result is, the once-close costars are at odds. “This is so uncomfortable for Lori because she’s always had such a great relationship with John,” notes the insider, adding that he stood up for her after she was arrested in the college admissions scandal. “But she’s done being the nice girl. She’s sticking up for herself from now on.”