You can admire and compliment but never touch a cosplayer unless requested to.
Obviously every con is full of beautiful people, some in more reveling costumes than others. But just because someone is showing more skin that doesn't give you or anyone the right to be inappropriate. Show everyone at con the same level of respect you'd show your family. You can admire and compliment but never touch a cosplayer unless requested to. Never cat call and if you have a photo taken with a cosplayer you should still avoid touching them.