Doing It for the Art: Nearly everyone in the film, but special credit goes to Benicio Del Toro, who burned his arm with cigarettes to match the burns on Oscar Acosta's arm, and ended up getting blood poisoning. He also gained 40 pounds for the role. He tried to put on even more weight, but there wasn't time.
Dyeing for Your Art: Johnny Depp had his head shaved to match Thompson's male-pattern baldness. By Thompson. With a straight razor. While Thompson wore a miner's helmet.
No Celebrities Were Harmed: Subverted by the first editions of the book, despite the best efforts of the publishers. When publication of the book was still being negotiated, the lawyers of the publishers tried to get Thompson to delete the references to his attorney engaging in criminal acts, since; even as depicted through an expy, could have badly damaged his reputation and been considered libelous. Thompson reached out to Oscar Zeta Acosta; the real life model for the fictional Dr. Gonzo, and asked him to sign a release. Acosta however initially refused. Not because he was concerned over libelous content, but because he took offense at being portrayed by a fictional version of himself. He would only sign the release on the condition that he be explicitly named as the basis for Gonzo on the book's cover. In other words, he insisted on taking full credit for the very criminal behavior the lawyers feared would harm and or offend him.
Mid-Development Genre Shift: It was originally just going to be a straight series of articles covering a motorcycle race in Las Vegas, before becoming the weird, wacky, genre-defining whatever-it-is that it became.
Famed animator Ralph Bakshi wanted to animate a version of Fear and Loathing based on Ralph Steadman's illustrations. Hunter had given the film rights to one of his girlfriends, and couldn't dissuade her from making the live-action film instead.