I see shirtless men on bicycles pretty frequently on the local MUPs here in CO, and could really do without the views. At the very least, if you're going to go shirtless, be sure you have some physical attribute to show off other than your unsightly fat. It's not attractive or cool to watch a grown man's fat ripple as he cycles over bumps.
The worst was last week, when I passed a 60+yo man cycling in sandals, what looked like a speedo, and nothing else. Nasty. Awful. Right down to the massively-overdone, sickly-looking tan. You. Are. Nowhere. Near. As. Hot. As. You. Think.