[Opinions] Re: frankly ...
I don't think it means "femininity is being identified with weakness." Nor a "symptom of societal sexism."
It's just kids who think they have to express gender in certain ways for it to be valid, trying to make each other feel inadequate for not expressing gender to their simplistic standard. They try to apply the pressure they feel, by denying recognition of the gender you want to be seen as - and the simplistic way to do that is to name-call you as if you're the other gender. Nasty, but not sexism. It can happen among girls too, taunting each other for seeming unfeminine by calling them a boy's name - just not as much, because girls aren't as vulnerable to that kind of attack.
- mirfak