I’ll start - Bringing something to contribute to the day without checking with the host what is wanted/needed first. Results in additional unnecessary work for the host who has had to cover that item because they didn’t know it was going to be brought and food that doesn’t necessarily match the rest of the menu but people feel obliged to eat anyway - On a similar note, people asking what they should bring about 3 days before the big day - this is a BIL special - no thanks my big shop has already arrived and we’re all sorted now. - People who clear up in the kitchen but put things away in the wrong places rather than just leaving them dry, neatly, on the side. What else?