In my experience people are always horrible to each other at christmas, they decide the whole thing is all about doing things they don't want to do for other people, and then they're really shitty about it and make damn sure everyone around them suffers and has a miserable time just because they've decided they have to do something they didn't want to do. Given that it's often the only time in the year that you get to see some family members, I'd much rather people just did what they wanted and were nice to each other.