Michael Rapaport says that sore on his lip is NOT herpes -- and now he's suing Barstool Sports claiming the media outlet and its most famous staffers are defaming him.
Rapaport used to work with Barstool -- in fact, he had a podcast on Barstool's platform.
But, the two sides had a nasty breakup back in February after Rapaport referred to "Stoolies" as "losers in life."
Barstool president Dave Portnoy told TMZ Sports at the time the move was not a publicity stunt -- "To me, it was very personal. It was very real.