The one I hate now is the middle school day before invite to a party. I will not let my daughter go to a party if the invite is not done by parents and that is done the day before the event.
Why not? This is how middle schoolers operate. Despite pleas for my girls at that age to plan things in advance, communicate better, etc, this was their social norm. Their social lives are just more spontaneous. They are starting to enjoy more independence, and they don't want to be burdened with calendars (sometimes this backfires, but then it's a good natural consequence) As long as parents are chaperoning if at someone's home, at it doesn't cause a huge inconvenience, I've got no problem when my DD is invited to a gathering last minute.
When my daughter was having a 13th birthday party, she was completely opposed to any kind of paper invitation. She insisted she would do them herself on Instagram, because everyone does that! I said OK, but asked that she ask parents RSVP me by text. Only because we were doing a sleep-over party at a hotel (very small number of kids!) It worked out fine, some RSVP right away, some in the middle, and some you had to follow up last minute with, which is typical. This year when she turned 14, she just wanted some money to go treat a friend out after school to fast food and manicures. All she wanted to do was ask a friend or 2 at school at the last minute, to avoid all the drama, and pressure of not leaving anyone out. So I gave her some money and let her be spontaneous.
When my kids were younger and get invites, I would always RSVP by the deadline, but usually not until right before the deadline, unless I knew the family well enough that we already talked regularly. Sometimes I was just plain lazy, and sometimes it was because life is crazy, and things can change, I didn't want to commit until the time got closer, especially if it was one of those very large "whole class" parties. I really did try to make it to as many as possible because you never know how many kids show up, and I never wanted to see a little kid's heart broken on his/her birthday.