Telling a guy to "Man up" is basically the same as telling a woman to "Get back in the kitchen.

I've been told to "Man up" by people in the past, especially when it came out that I was depressed over some issues in my life. It annoyed the hell out of me back then, and looking back, it still annoys me that just because I'm a man, I'm expected to be strong all the time. It's just as bad as telling a woman to "Get back in the kitchen" because she wants to pursue a career in science, engineering, or be in a management position.