Basically, Glover showed up for his interview promoting River's Edge dressed as Rubin, from the then unreleased film Rubin and Ed. Glover took the stage in groovy clothes, platform shoes and a horrendous wig. Unfortunately, Letterman and the audience had no clue what was going on, and when one audience member (who may or may not have been planted) heckled the actor, things went from unusual to downright strange.
Glover flips out after the comment, talking about how the press twists things around and then tries to prove it by reading stories about himself from a Los Angeles newspaper. The funny part is the comments in the stories seem pointless and out of context. Letterman, clearly not in on the joke, looks lost -- even turning to band leader Paul Schaffer, who wants nothing to do with anything happening onstage. Letterman asks Shaffer if this is the first time he's watched a guy drown. Glover just keeps going though, eventually challenging the host to an arm-wrestling match (Letterman declines) and then nearly kicking the gap-toothed comedian in the face while telling him "I'm strong ... I can kick!"
Letterman bails on the segment at this point, walking offstage and the show cuts to commercial. When they come back, Dave spends a few minutes talking about what's transpired -- and it's almost funnier than Glover's antics. Clueless, Letterman calls Glover a "dork" (much to the audience's disapproval). When the audience boos his comment, he asks if they would want to have dinner with the actor.
Memo to Dave: You might wanna check out this Andy Kaufman guy -- the kids love him and he did this kind of cutting edge act since the '70s. I'm sure a comic genius like you already knows this, though.