Mask off onboard the airplane right now? Depends on each carrier's latest protoct but for the most part you'll get mask shamed by a combination of personal, polite requests to your face and passive-aggressive "this is your captain speaking" public announcements for everybody around you to wonder who the problem child is. You might get tagged in the system for worse if you're overly disagreeable about it or you might not (like they won't sell you a ticket in the future). Maybe they'll take a harder line about it a few weeks from now or maybe who knows what.
The 6' thing is a lot like a WEZ concept. I don't know why this one is so hard for some folks to understand. If you're 30.1 miles from an SA-X battery or you're 29.9 then no, that's virtually no difference in your chance of getting shot. Sometimes the system gets a lucky kill that's a few clicks beyond even its max theoretical range and sometimes it gets an unexpected miss even in the sweet spot of its 99% or 95% Pk zone or whatever. But for the most part the odds of it working come down to math, really simple math.
Or think of it as what the concept of "max effective range" of small arms. Whatever works to make the concept click inside your head.
The other important thing about so-called social distancing is some of the science people think that viral load has a lot to do with how hard you get hit with the infection if and when you catch it. They think that is one possible explanation for why seemingly healthy medical people working in the covid wards have had a worse time of it than the data for the rest of the population would have predicted or suggested. Maybe it's a bogus theory but for now it certainly seems reasonable.
Riding in the back of an airliner you've got a vent right over your head blowing a mix of HEPA-filtered cabin air and fresh bleed air. You might as well point it directly at your blowhole (I thought everybody knew this life hack years ago). Whatever viruses or germs your sick seat neighbor is breathing out will go anywhere but into your eyes, nose, mouth, and lungs. Or you can close that vent if you want to be an idiot. With the vent blowing you're still inside your infected neighbor's WEZ but your odds are a heckuva lot better. And if you drew the short straw and it's Sneezy McSneezeface then their mask isn't going to catch 100% of the crud they're spewing but it will stop something more than 0.
Or pay for a whole row of seats or your own private airplane or whatever.
All this is the exact same idea as "don't get too close, I think I'm coming down with a cold."