I don't put on singlets. I see putting on singlets as old fashion and not what I should be doing. I want to feel free always and putting on singlets ruin that for me.
It depends on the material of the singlet. If it's not pure cotton, I will never put it on. This is because pure cotton feels cool on the body when it's inside unlike any other materials.
I don't see anything wrong with putting on a singlets as a guy. It makes you look stunning and cool each time that you dress. It is something every man out there should see as normal as long as the weather permits that.
The weather determines if I wear one or not. I rarely wear one. In hot weather, I'd rather stay comfortable with just a shirt than deal with the extra heat from a singlet.