TMZ has obtained a copy of a demand letter from Gina Gershon to Vanity Fair. Make no mistake - she's pissssed. Vanity Fair just published a pretty scandalous story about Prez Bill Clinton. The demand letter claims the article "outrageously insinuates that Ms. Gershon has had an inappropriate sexual relationship with President Clinton. This is absolutely false." The letter demands "a retraction and correction."Gershon's lawyers from the bulldog firm Lavely & Singer noted that "Gershon has only been in the same room as President Clinton on three occasions," all with many others present. The lawyers take a shot at Vanity Fair, claiming, "Rumor-mongering was substituted for fact-checking."