when you pull on a shirt of a certain material, causing a section of it to stick out and stay that way until smoothed out.
Person 1: "It's so hot out my shirt keeps sticking to my stomach" *pinches / pullsbottom of shirt out*
Person 2: "Now you have a shirt nipple"
By Miguelita
New Shirt Nipples
When someone forgets to iron out the creases that intersect at the nipples on a new dress shirt. They are seen most often at weddings and other formal events where people who rarely dress up are forced to.