This loop is located at the center top on the back of some mens dress shirts
The hook is for your thumb. If the weather gets too warm and you want to take off the outer shirt, then you can just hook your thumb in it and throw it over your shoulder.ha! ha! Tell you the truth, I honestly don’t know. But sounded good, huh?
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Editors Comment: Close – The loop is called a ‘locker loop’.
The locker loop is added fabric loop positioned in a high position, usually where the pleat meets the yoke, in the center back on shirts. The purpose was so you could hang your shirt in a locker, by the loop so as to avoid the shirt from wrinkling. They were more common on sports or oxford button-down collar shirts.
Some brands used the locker loop more prolifically than other brands.