If a fart can get through two butt cheeks, underwear, and a pair of jeans.. How are masks going to save is from Covid-19?
Because it's water droplets that infect us, not air. Your analogy would make more sense if you were talking about shitting yourself. If you let a fart go that turns out to be something else, it's unlikely to make it through your underpants and your jeans. But if you're wearing nothing at all, well, suddenly you've got shit running down into your shoes.
Well, let's be precise. If you can smell a fart, it's because shit molecules are indeed getting to your nose - or, to be even more precise, the methanethiols from the shit molecules are making the trip from the shit to your nose. That's how smell works.
However, the COVID-19 virus is between 100-1000 times the size of methanethiol molecules. So COVID is too large to hitch a ride on those molecules, let alone the viral load needed to overcome the body's defenses. So, as LTG points out, COVID hitchhikes on water molecules.