Well I really like the ripped shirt, but the right under arm has a fairly large hole in it, so as not to expose that part of my arm, I am wearing an under shirt. The sole purpose of an under shirt is just to have something under your clothes for a few different reasons such as "Layering" which can be seen as a style of clothing, or just putting on multiple layers so you don't get cold. I am using both of these aspects. It looks good, and it keeps me warm since I have to stand out in the cold for about a half an hour at 6:30 am.
The under shirt is a tight fit, and it is not really meant to be worn by itself. It is just a blank shirt that has nothing on it. It's not really meant to be looked at.
Take tuxedos for example. Normally, one would put some sort of under shirt under the button down.