So normal — square, even — as Marty McFly's father in Back to the Future, Crispin Hellion Glover (apparently that's his real middle name) turned in a thoroughly bizarre and completely uncomfortable performance during this 1987 appearance on Letterman's show. Ostensibly there to promote his film River's Edge, Glover babbled haltingly and read random clips about himself from Los Angeles society pages, all while wearing hippie pants, an off-kilter wig and platform shoes. It remains debatable as to whether it was all a performance (some have speculated that he was dressed up as a character from his future film Rubin and Ed) or if he was actually on some sort of drug. Letterman miraculously allowed Glover's rambling to go on — until Glover almost kicked him in the face.