A hypothetical "ID card" that indicates that someone is a "real man". Used most often in a self-effacing manner when performing some supposedly "unmanly" deed, but occasionally used to mock another man (usually a close friend, said in jest) who has done or is doing such a deed.
"A lady just asked me where to find something in the arts & crafts department, and I was able to tell her exactly where it was. Where do I go to turn in my GUY CARD?"
"John, what are you doing watching this chick flick? Surrender your GUY CARD immediately!"