I dont think it's the change that makes people angry as much as having to correct themselves. To me it is just a case of you say toe-may-toe I say toe-ma-toe.

When I say Christmas vacation I mean winter recess, and whenever I refer to Christmas it's not against anyone to join in the festivities, because what I am celebrating is not a religion thing, but a human thing. The gathering of friends and family for pure enjoyment. Who cares the historical importance, I say just have fun and stop ruining it for everyone else by pointing out that you don't agree with what the textbook definition of what we use to describe it is.

In the same way it's not a religion thing why I don't like people who point it out, it's a human response to them getting on my nerves by "correcting" me.