Where did the Peanut Butter and Jelly song come from?

Answer 1

Early childhood memories.

Answer 2

Glasgow Gorbals area.
I should explain for those who don't know.
The gorbal area of Glasgow was redeveloped into lots and lots of high rise flats with play grounds for the kids at the bottom. and kids didn't want to got all the way up all the stairs to their mothers for lunch so they would call up
"ma, chuck 'es doon a jelli peice"
Or a jam sandwich if you want to be posh

so the mothers would wrap up this sandwich and throw it out the window to their kid waiting below.

now due to wind between the highrises, and the speed the packages reached the ground at, not all of them made it to the hands of the correct kids or to the ground at all. some landed on ledges on the surface of the buildings, others got grabbed by gulls , some actually made it to the ground, but hit the ground with enough force to spat the snack.

so as the song goes. "the odds of it reaching ground are 99 to 1"