Former "Teen Mom" Farrah Abraham staunchly denied the existence of a sex tape ... and then flip-flopped ... and then threatened legal action ... and then said some REALLY dumb stuff ... and TMZ caught the whole thing on tape.
21-year-old Abraham was shopping for sexy lingerie at Agent Provocateur in L.A. yesterday when we asked if she knew about the existence of the sex tape being shopped around town.
"I don't ... exist ... anything about that," Farrah eloquently told us.
Farrah later changed her position ... saying, "If I had my own personal stuff, that's my own personal thing."
During the encounter, we learned Farrah doesn't know the meaning of the word, "elaborate" -- ya gotta watch the video.
We broke the story ... a sex tape featuring the MTV star is being shopped to various porn companies, including Vivid Entertainment. Steve Hirsch, President of Vivid, tells TMZ he saw the video and confirms Farrah is featured in the footage.