Massive cultural pressure, peer pressure, and pressure from women in general "educates" us men from a very early age that we'd better not be feminine. Then it's up to each of us to work out how much of that crap we are prepared to buy into and still be true to ourselves vs. how scared we are of being rejected/beaten up/humiliated/etc. in a particular environment.
I moved to a fairly working-class area of Cambridge (England, that is) 10 years ago, and I had guys shout "->-bleeped-<-got!" and throw stuff at me out of car windows, just because I had a white jacket on. I got rid of the jacket, and survived. We're really powerfully conditioned, and it's a lot stricter for men in a more working-class social climate, for some reason.
What I look for in a man or woman is that they be themselves, "masculinity/femininity" notwithstanding. If you want someone to behave a certain predetermined way in order to shore up your own sense of identity, then you're trapped to some extent too. If that sounds a bit blunt, well so be it - I'm tired of a world that conditions men to behave a certain way and then rejects us for doing so (as I'm tired of catching myself trying to behave that way in order to feel safe). Let's all let ourselves just be ourselves.