Definitely Christmas dinner. Not doing it this year. 3 hours in the kitchen/not relaxing, and an hour clearing up after. OK DH clears up usually, but that's 4 hours wasted on Christmas day. (And an hour to eat it all... so 5 hours really..) DH was a bit disappointed when I said I CBA with Christmas dinner on Christmas day, so I said, 'well you do it then,' and he was like 
He wants it but doesn't want do it, so we compromised and said we'd go for a Christmas meal at the pub, (on 20th December) and then have a pizza between us on Christmas day, or a Pukka pie and some peas. Sorted.
I have done it for 30 years, every Christmas day (Christmas dinner, and wasting 4-5 hours of Christmas day on it,) and I am tired of it.
None of our DC live at home now, and we see them for an hour in the morning and then come home at midday. So it's just me and DH. And as I said, he doesn't want to do it, and I'm not doing it, soooooo... the pub it is!