I think it's safe to say Tom has finally pulled the plug on the Pigpen rap. I just heard how this whole thing started. Mike thought it was great and wanted Tom to hear it. Said he was the "first Rapper." Mike liked it. He actually liked it. Mike playing this for Tom was a golden moment in the show's history. Mike liked it enough to give it to Tom. And of course Tom was like "this is terrible" and then the stage was set.
Hold on. You don't think I knew what Tom's reaction would be?! Also, although I am a fan of the Grateful Dead, that doesn't mean I'm a fan of everything they did and can't recognize their excesses, including Pigpen's raps, as possible comedic gold. What I did was tee one up for Tom and watch him hit it out of the park (see the Cowboy Star show for another example of this). Give me some credit, will you.