I work in a school. One of the other teachers is leaving. They have invited a group of people to their leaving do and left a few out. The people who have been invited are various ages and job positions (SLT, TAs, Teachers etc) she has basically just excluded a few people she doesn’t like (including me). I have never had any conflict with this person, there is no back story that I know of. I am often excluded from things but never with so many others being included. Usually about half of us aren’t invited. We are also having a lunch on her last day, that is for everyone. She didn’t organise the lunch.
YABU - it’s her leaving do she can invite who she likes
YANBU - it’s a dick move