1. It refers to sunglasses with black frames which have clear lenses and no grade. It is a fashion accessory that make buff or masculine men look geeky. When the (sun)glasses are taken off, the geeky looking buff men now look like superman.
2. Masculine or buff men who wear sunglasses with black frames which have clear lenses and no grade that makes them look geeky. But, when they take off their (sun)glasses, they look like superman.
1. Those Clark Kents disguise his true masculinity just like Superman.