"Man" is the term given to human adult males. Meaning they have an X and a Y chromosome. Attaching any other requisites to the term is nothing more than adolescent posturing.
This is actually something I've never understood. I lost track, while going through my teen and early twenties, of how many times someone would try to get me to do something by attacking my "manhood." "If you were really a man you'd do it!" and what not. Needless to say their attempts always failed. I have been self-conscious and insecure most of my life, but never about that, which makes me wonder why others are taken in by it. In fact, it often seems that the people that society would dub the most "manly" (i.e. bodybuilders, jocks, etc) have always been the ones most intent on proving their "man-ness". If I had to venture a guess I would say that it's because the ideology of proving one's "manhood" is a self-defeating one, because it's based on social comparison. There will always be someone stronger, or tougher, or sexier so basing your self worth on how you compare to others is asking to be put down.