Thing is girls aged 12 to say 16 or 18 ARE vulnerable.
At the younger end they are children.
Most girls when they're young find this sort of thing embarrassing and intimidating. It's an age when many girls are very self conscious (boys are too, not a sex thing but a teenager thing).
By the time I was 16 I'd had enough of this stuff to just ignore it/ let it wash over. Because I was used to it. It was a normal backdrop to life for me and my friends.
That's not in any way good, is it. It's not positive to roll your eyes when an adult man says something obscene to you on the street or exposes himself to you, because you're used to it.
Also from about 15 I was a bolshy sod. Yes men prey on those they perceive as/ know are vulnerable. That's why girls with disabilities have such high rates of abuse. Yes it's good for the girl who doesn't get anything (although I doubt it's due to giving off certain vibes!). But he'll do it to someone else instead. Someone he does perceive as vulnerable.
The doubt the best to look out for yourself is good of course. But it's what always gets focussed on and to me does smack of victim blaming. EG a girl with profound disabilities is assaulted by a man. The underlying thought of well, she's vulnerable... (And so what can you do... Is the subtext that I think is often not recognised).
Anyway I was a bolshy sod and I can tell you for a fact that many of these men become very aggressive if you don't react how they want you to/ say something rude to them/ tell them to piss off.
I always wonder at the give back as good as you get thing because IME it is a dangerous tactic. And one that is doubly so because like it or not, a grown man will usually have a physical advantage. Especially if the person who refuses to be upset/intimidated (which is what they like) is a 16 yo 7 stone schoolgirl.