My top one is people who do NOT RSVP, or people who don't RSVP til asked, then say they're coming and don't show up. These same people have the nerve to ask for an RSVP at their own parties. Second place is people who don't respond at all. And third is people who make comments like "sounds like fun" and then there is nothing further and they don't show up. We all know how much time and effort is involved in throwing a nice party, and with my baby food I absorbed the fact that when you are invited somewhere, you say whether or not you are coming, politely cancel if for some reason you can't come, and if you do come, offer to bring something. Why is that so difficult????? Once my daughter went to a birthday party where several guests had said they were coming; none showed up but my daughter. I felt terrible for the Mother, not to mention the little girl....