We invited my fiance's Aunt, Husband and their 16 year old daughter. We received the RSVP back with 4 people which included their 16 year old's boyfriend. I don't know him, have never met him and neither has my fiance. We had never even HEARD of him until the RSVP came back. I contacted her and said, "While we appreciate the RSVP, in order to accomodate both sides of the family we'd really appreciate if you just kept your guests attending to 3." She responded back with, "There WILL be 4 because we already told him that he could come. I feel like it would be rude to tell him that he can't come. I thought the RSVP was to tell you how many people were coming." That really really really ticked me off because a) why the hell does he care who we are and if we get married?! We don't know him. b) she completely disregarded my respectful request to keep their guests to 3 people and c) IT'S MY WEDDING! Not yours! I couldn't keep it in anymore and responded with "Well, that's fine but he will have to sit with people that he doesn't know because our seating arrangement is now done. Also, it's incredibly rude to take it upon yourself to invite someone to our wedding. So it's on you for being rude. The RSVP is to tell us how many are coming, people WE invited to OUR wedding. She then called my fiance's mother to say she's retracting her yes! She couldn't even tell me!
tl;dr: people are rude.