I like the parody of Tom Paxton's "The Last Thing On My Mind" that was written for his 60th birthday: "I Don't Know What Was The Last Thing On My Mind."
Then we must not forget the takeoff on "Dona Nobis Pacem" that goes
"Don't I
Know this
Possum, possum?
Don't I
Know this
Po-o-o-os-sum?