So, what was the first videogame music "joke?" i.e. a bit of musical theme that is doing something funny on purpose?
I think it's a toss-up between
https://www.youtube.com/watch?v=4_gObHt1uZA <-- Tim Follin opening with a down-instrumented version of the kind of fantasy theme that Dragon Warrior and Final Fantasy had, and then stepping all the way on the gas
https://www.youtube.com/watch?v=V2k01qmi99k Comparing the NES version of the Metroid escape theme to the Famicom version of the theme (https://www.youtube.com/watch?v=WLpz_yNIT_o), the original Famicom version has an A-B-B loop structure while the NES version introduces a C part (A-B-B-C). The C part sounds very reminiscent of the themes from Kid Icarus; Hip Tanaka scored both games and the version of the escape theme for the NES originally appeared in public as a B-side track on a game music compilation released in Japan. I think it's either a nod to the game's shared lineage (same composer, same "engine," same dev team), or a nod-and-wink that the end of Metroid is just an enemy-free Kid Icarus level climb.
Are there older examples?