Yo, Mardi Gras is a street festival in New Orleans at the beginning of the christian observation of Lent. Lent is supposed to be a period of self-denial, so Mardis Gras (Fat Tuesday) is a monstrous party of self-indulgence. The culture surrounding Mardi Gras extends far beyond the festival itself, though, there's a whole tradition of music derived from the bands that march in the parade, which is where the song "Brother John" comes from. Dave didn't "steal" it or anything, but he didn't write it.

WillH, thanks for the tip on the film -- I'll see if the library can track it down for me, I'd love to see it.