You workout on a regular basis, you watch what you eat, you don't smoke, you don't drink excessively.... You know what, you are so good to your body that you should kick back and relax a little bit. Why not have a seat? A-HA! You fell for it. (I knew you treated your body like garbage.) Sitting is horrible for you! Get your ass off that couch. You're killing yourself... literally!
A recent Australian study found that "those who reported sitting for at least 11 hours a day had a 40% higher risk of dying within the next three years than people who sat for less than four hours a day."
And no, exercise does not absolve you. Regardless of how active you are during your non-sitting hours, sitting too much is still horrible for your health.
The upside of all this is that the next time someone steals a seat from you on the subway, you'll know they're going to an early grave.