T-shirts

Ever since the 50's, t-shirts have gone from a military undergarment to a closet staple. Like most styles of the century, the t-shirt rose to popularity after people saw it on the big screen in movies such as A Streetcar Named Desire and Rebel Without a Cause.  
Just about everyone has worn a t-shirt, and it's not hard to see why. T-shirts are cheap, comfortable, casual, and can be worn with just about anything. 
The rise of screen printing made it possible to have custom t-shirts made for any occasion. It wasn't long before marketers started using printed t-shirts to advertise too. 
I doubt the classic t-shirt will ever go out of fashion. They might not be considered faionable, but these easily customizable, casual garments have quickly become a part of American culture. 

Sharon Stone wearing a Gap T-shirt on the red carpet in 1996
from usmagazine.com