Phish.net

"Mean Mr. Mustard" is a cryptic character sketch from side two of The Beatles’ legendary Abbey Road album (and the second song in a four-song progression commonly called “The Sun King Medley”). The lyrics describe a man of ill habit and nasty demeanor who (in Phish’s mythology, anyway) might be found fraternizing with the likes of "The Sloth."

Phish performed “Mean Mr. Mustard” only once, and near the end of a second set in which, curiously, every song but one had a word in its title starting with the letter “M.” In a charmingly bizarre nexus of Sesame Street and "Shakedown Street," Trey announced that the set was “brought to you by the letter ‘M’ and the number 420.” Apart from its alliterative impact, the cover was also noteworthy for the theatrical guest appearance of John Popper, who portrayed Mr. Mustard in cape and cane before joining in on harmonica for the one-of-these-things-is-not-like-the-other “Weekapaug” closer and “Funky Bitch” encore. 

Watch Mean Mr. Mustard on YouTube Phish, "Mean Mr. Mustard" > "Weekapaug Groove" – 11/15/96, St. Louis, MO