I just played with some guy who randomly started spaming me on real ID invites. This was kinda annoying as I was playing with him and didn't want to be rude and decline him. I never gave him my battle tag nor Email. So how is it possible for him to add me there?
I am very casual to the game at the moment and haven't had time to get to know all features, so don't flame if the answer is too obvious.
Edit: Is there a way to hide my battle tag, or online status?
I believe there is an "Add Battle-tag" option if you right click someone's name. Don't think there's a way to stop that. You could tell him that you're uncomfortable giving out your battle tag and request him to stop.