For a while now, depending on who you talk to, I've been known for wearing plain white t-shirts. In the hot, muggy, South Louisiana weather, keeping cool is vary important. That's where the simple white shirts come in handy
My plain white t-shirts aren't just plain white t-shirts, however. They are undershirts. Size large, hanes, crew neck, undershirts. And I never leave home without one.
Undershirts are not like regular t-shirts. Typically, they're made of a lighter weave, rather than the thick weave of a 'heavyweight'. This makes them ideal for wearing in hot weather. Nice and cool and breezy.
Something to keep in mind is that they are designed to be worn under other shirts. Undershirts... Get it? They come in two main styles: crew neck and V-neck. V-necks are, just as they sound, shaped like a V at the neck. They're designed to be worn under dress shirts when you don't want the collar to show and would rather your chest hair peak out at the top. I prefer the crew neck, myself, because they're more acceptable when worn without an overshirt.
Another thing is that the sleeves are a lot shorter than normal t-shirts. You don't want the sleeves of the undershirts sticking out from under the overshirt. You want them to be unseen as much as possible. Unfortunately, the sleeves are so short that when I'm not wearing an overshirt, my armpit hair sticks out when I lift my arms up. Not that I do that much. And even then, I get a nice breeze in my pits. Very refreshing.
Of course, I only wear an undershirt with no overshirt when it's really hot. Just the undershirt alone is typically inappropriate for a night on the town or work. Plus, since it's such a thin material, it's semi-transparent. Which means you can see my nipples. Which is not something I like to show off. My manly chest hair, however, is a different story.
From a practical standpoint, the utility of wearing an undershirt as an undershirt cannot be overlooked. It provides an extra layer to separate your body from your outer garment. Even though I wear antiperspirant deodorant, I, like most people, still sweat at the pits (and back and chest) when overheating. The undershirt will absorb a lot of the sweat, preventing it from soaking through to the outerwear, possibly ruining your good shirts and causing much embarrassment. Also, as a larger (read: chubby) guy, I'm a bit self conscious about certain unnatural folds and creases. An undershirt provides extra padding that equalizes the fatty bits, preventing jiggling and causing a more stream lined appearance.

Keep in mind that no amount of protection can completely prevent these problems. A little sweat may show through. A pot belly may still be apparent. The idea is that it subdues it. Disguises it. Makes it not so obvious. Nothing can help more than a healthy diet and a bit of excercise (or prescription strength antiperspirant if that sort of thing is a problem).
A lot of people wear A-shirts, or Muscle shirts, or wife-beaters as undershirts. This may be useful for the equalizer factor, but does nothing for the pit stains. Also, you look like redneck trailer trash when wearing them alone. I don't really see a point in that. Another variation is the long-sleeved variety. In the south, where temperatures rarely get below 50°F, long sleeves are impractical when a hoodie or light jacket would suffice. For these reasons, I will stick to my tees for the time being.
In conclusion, undershirts are an essential part of any man's wardrobe. It provides enough coverage so as not to be arrested for indecent exposure on a hot day and acts as a second layer of protection in between your outfit and your bare skin. I highly recommend Hanes 100% cotton crewneck, but it's really a matter of personal preference.
Until next time,
~Ben