Why is it "not cool" for a man to get upset/teary at certain things....?

Most guys need to appear strong even if they don't feel it at that time. I don't necessarily think that men shouldn't cry at some point in their life, but those times should be rare and for a good reason. Women especially want a man who can handle all their emotions and problems, plus be able to deal with their own problems themselves. My girlfriend right now is very supportive, but even she doesn't like a crybaby. Being the rock in a relationship is just the role that men play in the world and it isn't going to change. Thats why you need to appear tough.