I can't believe I'm commenting on this. I need a new hobby.
Let's assume that Meelo will, at some point in his life, master the previously-nonexistent "art" of the one-gun salute. Let's also assume that this practice involved exactly what we think it does...expelling large amounts of air, at great speeds, from the ass (obviously), to achieve any number of goals (vertical propulsion, knocking an opponent to the ground, slapstick comedy, etc). And then let us also put aside for the moment that all of these goals could be accomplished with common airbending skills and without the need to airbrush one's boxers. Depending on Meelo's level of skill, his ghost turds could be pretty substantial, and given his personality, he would be making regular deposits at the stank bank. Unfortunately, as skilled a bender as he is, his body just wouldn't be able to keep up. He's still only human, and that's a lot of wear and tear on his trouser tuba. Incontinence would set in before he was in his thirties. After all, every foul howl is just a turd whistling for the right-of-way. He's already developed a habit of shitting his pants (when Pema asked Lin to bathe him at the end of Season 1), and I would imagine that he would soon learn the harsh lesson that after the thunder comes the rain. In the end, it's just not worth the trouble.
Jesus Christ, I can't believe I just typed all of that. Someone needs to get himself laid.