LISTEN to those around you, they will offer you a good point of view to something you probably can't see on your own. We as supposedly open minded individuals (Come on, we watch things with non existent technology, time leaps and magical girls!) should be the one's to see that there is a point to some of what our parents our siblings are saying.
This is a general thing, when in public do not talk in such a loud voice that the person peeing at the farthest cubicle can hear every bit of your conversation.
Keep private matters private, even if you're so goddamed proud of what you did with your wig and how you had to save it to make it look like it does. As for changing into costumes, do not occupy an entire sink just for your stuff.
That isn't your bathroom. It's for everyone! And if you don't want people wanting us cosplayers gone from those areas then the best we can do is share and be polite about it. We aren't paying anything extra to make use of the public toilet so we shouldn't be expecting special treatment. And when a guard is yelling into a megaphone straight into your ears, resist the urge to kick or yell at him and simply do what you're told.
Though a friendly, "Kuya/Sir I can hear you just fine" with a laugh even if the guard looks mean or pissed wouldn't hurt.
From Admiration to Stalking
Just imagine, if you had a little sister, and she tells you that a group of guys are blatantly waiting for her outside of the comfort room area or in a staircase to her class or office wouldn't you fear for her? A GROUP OF GUYS WAITING is never a good thing more so if you don't even know them, it's one of the scariest things to actually experience.
If it's something that would cause someone discomfort or fear, than that's definitely stalking. Conventions are different as people there are in the area for good reason, to share a commonality that is the hobby. But to randomly approach a stranger just because they look like a 'cosplayer' or that she or he is REALLY so goddamned cute, is NEVER a good thing. THERE ARE PLACES to make friends and outside a comfort room is NOT IT. Or a staircase or an elevator, if you make the person feel like they're 'cornered' into talking to you. That won't lead to anything good, it might even get you into prison for harassment.