I think I got to the Lonely Goatherd parodying first, way back in the late nineties with What If Rodgers and Hammerstein, instead of writing The Sound of Music had written Assassins.
High on a hill stood a lone assassin
Layee-Oh-De-Layee-oh-de-layeehoo
He shot the Pres while the Pres was passing'
Layee-Oh-De-Layee-oh-de-loo
Oh, oh, did you hear a gunshot
Oh, oh, from the grassy knoll
Oh, oh, was there only one shot
Well, why don't we take a poll
etc.