Not because I'm worried they're going to give me covid, I'm wearing a mask and I'm vaccinated and I'm not getting that close to them. But, I don't know what they're going to do next. Someone who's not wearing a mask on the subway is someone who doesn't care about anything but themselves. Are they going to start littering, spitting on the floor, on me? Will they just take off their shoes and start cutting their toenails? Will they drop trow and just take a dump? or maybe they will just light up a cigarette? Why not?
Seriously people, you are sharing the environment with people just cannot get vaccinated. They are called children and they are everywhere. (Rarely, there's the person who medically cannot take the vaccine. More commonly there are people who think they shouldn't take the vaccine for medical reasons)
Maybe I'm taking a leap, but that guy not wearing a mask is probably more likely to be the guy that's not vaccinated. So, he's not unlikely to be spreading the virus. And even those that are vaccinated can inhale it and exhale it on someone later.