- Be respectful if you want to take photos of cosplayers (most cosplayers are more than willing to pose for photos. be respectful if they say no, be careful of their costumes as they may be fragile and you don't want to damage it and be extra gentlemanly towards female cosplayers, regardless how skimpy their costumes may be)
Also, even if they are acting suggestively towards you, do not take this as a sign to reciprocate, unless the suggestive behavior is being done in private. Many of them do so simply for the photos or to maintain the appearance of availability to draw in others willing to take pictures.
If you wish to have a specific pose with a cosplayer or celebrity (such as putting your arm around them), discuss the idea with them first. If they say no, drop it and leave it at that. Never assume that you can just do whatever.