Crispin Glover on Letterman
Date: July 28, 1987
Evidence: The first symptom is the wig. We're not sure what George McFly's hair looked like prior to this interview, but we're pretty certain it didn't look like that. Then there's the clothing. He's dressed in striped pants, a heinous purple shirt and a pair of black platform shoes that don't appear to fit him. Keep in mind that this is '87, not the early '70s. If you're wearing what Crispin Glover is wearing during this interview, then you've clearly been high long enough to have gone shoe shopping while fucked up.
As far as behavioral symptoms, we're not really sure how to describe what Glover is doing here. At first he seems to be terrified of Dave and the audience, but then he challenges Letterman to an arm wrestling match and tries to jump-kick him in the head.
Drug(s) They Were Probably On: Difficult to tell. At first it seems like a classic acid freak-out. He is looking at Dave like he has three heads and the audience like they're a big tangled lizard orgy. But then he starts getting physically aggressive. Our theory: a second drug along the lines of PCP, taken right before he went out, kicked in halfway through the interview.