Mozart was definitely not the serious person some people think he is. He was a drunk and a troll who loved poop jokes. There is the masterpiece OP mentioned but there is also the "sequel": "Leck mir den Arsch fein recht schön sauber" ("Lick my ass right well and clean") and he also wrote a piece called "A Musical Joke" which is full of dissonance, exciting build ups that lead to nothing, wrong keys, "wrong notes" etc. just to make fun of the musicians playing it and other bad composers (funnily enough while trying to make music that sounds bad Mozart ends up using, for one of the first times in history, politonality a technique used very often during late-romantic and early-modern music.
WHERE THE FUCK IS THE SHEET MUSIC SO I CAN PERFORM THIS MASTERPIECE AT MY GRAD RECITAL?!?!
Mozart loved his ass jokes. [He even composed a melody for a particular singer in faux Latin,](https://en.wikipedia.org/wiki/Difficile_lectu) knowing his thick accent would render "Lectu Mihi Mars" as... well, "lick my ass", as well as including a portion where the word "jonicu" would be repeated rapidly in a way that would make it sound like "balls balls balls balls balls". The audience would then turn over their programs and sing another composed melody about how silly the singer was.
Idiomatically, it's closer to "kiss my ass" or "fuck you"
I've heard of a Mach piece called ["Lick My Love Pump."](https://media.giphy.com/media/Y2W94ORJI1lGE/giphy.gif)
Lick my flaps nicely, lick it nice and clean, nice and clean, lick my terryfolds. That's a foldy desire, nicely buttered, like the licking of roast meat, my daily activity. Three will lick more than two, come on, gonna eat those foldy folds, and lick, lick, lick. Everybody suck my holdy flappy folds for themselves.
Except for it maybe being some kind of Old-Austrian dialect, isn't it: Leck mich im Arsch?
Mozart was renowned for his musical jokes. One of my favourite stories is about an aria from Così fan Tutte called Come Scoglio. The official story is that the soprano who sang the role at the premier had a great bottom range and a great top range but wasn't fantastic in the middle so the whole aria switches between the two registers throughout (it's a bit of a nightmare to sing I have to admit!)
The unofficial story is that Mozart hated the woman singing the role and she had a habit of tipping her head back for top notes and tucking her head down for low notes. By switching between the two registers so quickly Mozart made the woman look like a chicken bobbing her head up and down.
I have no idea which story is true (or if neither of them are true) but Mozart certainly had a knack for musical jokes.
Slob on my knob
Like corn on the cob
\- Mozart (probably)
Here's the audio: https://www.youtube.com/watch?v=C78HBp-Youk