Hmm... flipside - as a gay man who does cosplay at cons and clubs and such, I actually quite enjoy all the attention, flirting, groping, come-ons, invitations, and yeah, even the snide whispers are kinda entertaining. Con time is party time, and every time I've gone to one and gotten dressed up, I get a lot more attention than I would if I was in plainclothes and it's really fun and a great conversation starter with other con-goers, which to me has always kinda been the point of going to a huge nerd gathering - meet other nerds!
So... I can see why the lines might be muddled for some people since that environment in itself is kind of meant to encourage social interaction. And cosplay is generally one of the ways a person expresses themselves at those events and usually the message is that they want attention and social interaction. And absolutely yes there is a difference between just talking to someone and verbally harassing them, but... even as a guy who is generally pretty good at picking up on social cues, some girls just get immediately defensive no matter how you approach them (even if you have zero interest in them sexually/romantically like in my case) and once you've made them uncomfortable there's no taking it back. Now, I can completely understand WHY some girls get defensive no matter what, because obviously not everyone is awesome like me and completely without ulterior motives so those women have been given good reason to be defensive. But it does make it hard to know where the line is between "Hey I'm being friendly" and "Hey I'm being a creeper". And I can sympathize with that.
But perhaps that's my privilege talking? I'm honestly curious how cosplayer girls feel. Surely they have at least SOME of the same desire to get attention? What's the actual line? How much of that line is based on the attractiveness/appearance of the person giving you attention? Because as a fairly attractive guy I know I've gotten away with a lot of stuff that I've seen my less-attractive friends get slapped for.