The phrase is directed at men who feel underpessure to live up to the societal expectations of masculinity and are insecure not meeting those expectations. The phrase is used to point out that their very insecurity about the issue proves that they are not a real man and do not live up to expectations. It is mean and nasty way to make their struggle even harder.

If a women was insecure about her appearance for example. This is likely to come from the unfair beauty standards placed on women but it would be nasty to tell her that she's just fragile and that if she was a real women she wouldn't need to prove it through vein attempts to live up to beauty expectations. That would be seen as really nasty and rightly so.

The reason people think its okay to do this to men and not womens is based on the assumption that men don't have feelings. Its mean to attack a womens insecurities because that would upset her. Its not mean to attack a man's insecurities because men don't have feelings and if they do get upset they should just "man up"

I know the defence some will make is that men put these expectations of themselves whereas women are given these expectations from men which is why its apparently different so I'll address this point.

Firstly I don't agree with that, there are plenty of mothers who don't make as much space for their son's emotions as their daughters and teach boys from an early age that their emotions aren't as acceptable. Also plenty of women in relationships who use their partners vulnerability against them in relationships. I won't claim to know the experience of women with beauty standards but from what I can see it also comes from other women and womens social media. These expectations are a society wide issue, not just something only men are responsible for.

However even if we assume that it is only men who teach boys that they can't have emotions and the image of toxic masculinity then that is still not an excuse for someone else to prey on those insecurities. If a man has been subjected to toxic masculinity all his life and then you use the insecurities this has given him as an easy trigger to make him feel bad about himself and not like a real man then you are just as bad as the men who taught him those toxic expectations in the first place. You are just piggybacking on the toxic masculinity men have used to make someone feel a certain way as an easy way to make someone feel like they aren't good enough.