I know this was a fashion trend in the 80s, but some guys wear half-tops for exercise today. My boyfriend does. I think it's hot on him, because he has a flat stomach. He mainly wears them on days he works abs.
I'm personally attracted to the male specimen , especially their abs, if they don't have a bloated stomach. So if they have the body then I don't see why they shouldn't flaunt it. It makes perfect sense if he's working out. Guys cover their bodies up too much these days! Just my opinion.