What makes a man a man ?

Been doing a lot of thinking about what it is that makes a man a man or a woman a woman, and honestly, I dont know.

I try and think of things that men do, and I can always find some men who dont like doing them, and some women who do, so what does it mean to be a man or a woman?

Is there something that is definitely masculine, or definitely feminine, that you can know if the person does it, they are without doubt a man or a woman?

What do you guys think?