When you’re on a crowded subway and you’re sitting right next to someone (ie. sides of thighs touching), it’s perfectly fine to scoot over to the next unoccupied seat when the train empties out. I think some people think, “Oh, if I move away from him, he’ll think I’m being rude and don’t want to sit next to him, so I’ll just sit here awkwardly right next to him with our thighs touching even though there are 4 empty seats on either side of us.”
So, go ahead and scoot over to the next empty seat. The side of your thigh will thank you.