A friend of mine recently told me that she and her boyfriend were invited to mutual friend's wedding a few years ago. Just weeks before the wedding they broke up and because she didn't want to have to sit at the same table as him (she claimed the only people either of them knew would be sitting at this table), she skipped dinner and then brought a friend to the dancing portion of the reception. She said in retrospect it was a bad idea, but I still told her I would be irritated if she had done this at my wedding. The bride and groom paid for her dinner, which she didn't eat, and then she brought an uninvited guest to the reception!
FI and I have already had to turn down a few of his friends because they are technically single. They all said they are dating but not in a relationship or they are in between several girls, etc...I hope none of them bring someone to the reception. Does anyone think this could happen at your wedding? I guess I wouldn't mind it so much if someone came after dinner, but it's still not appropriate.