Even if you are coming home after a long day at the office, there is no excuse to smell. If you're a parent, make sure your children don't smell. If you're a child, make sure your parents don't smell. If you're a husband, make sure your wife doesn't smell. And so on.
A caveat: Accept that homeless people will smell, and that the smell might be made stronger by the closed confines of the subway car. Rule of thumb: If you have a home, there is no excuse for smelling.