This is the fight song for Yale University, and was written by Cole Porter, Yale class of 1913. It is nearly a self-parody. However, Lehrer's tiny changes, consisting just of a few added repetitions of words at critical moments, throw off the musical timing in a hilarious way.
Recording of the original, by the Yale Marching Band (singing starts at 0:28)
Words as performed in the Physical Revue (Words in blue added by Lehrer. Words in red are in the original but not in the Physical Revue.) Sung by the entire cast:
Bull dog, bull dog,
Background image: covers from some of Tom Lehrer's albums