I know you have said your post is lighthearted - however,
I can't stand that phrase or the male equivalent.
I know you aren't referring to people with genuine issues but my experiences are...
I work with teenagers and typically find if one expresses that they are unhappy or struggling, they are told by their peers to (as you and they put it) , 'man the fuck up'. This i have seen as a response to worries about pregnancy, abortion, bereavement, sexually transmitted infections, abuse, bullying, exam stress, parental divorce, body image..
I just think it's the wrong way to deal with things and generally used by those who don't know how to help or feel uncomfortable. I am not saying that is you but it's my experience with young people. The ones who can't cope with emotion are the ones who block it by saying 'man up'.
People's problems are relative to themselves. What can seem easy to me will seem a nightmare to another and vice versa.. But when they find it difficult and I don't, I don't think that gives me the right to tell them to man up. Unless in a supportive 'don't be a doormat' type way..
We all have 'firsts', none of us are born with a complete guide to life and we all struggle with things/can be inclined to whinge or panic. Experience and support generally batts panic and moaning away.
But telling someone to man up generally fixes zilch. If anything, it causes more problems than anything. Even the bloody words emphasise the 'hard nut guy' image.. I just can't stand it.