What is a good way to handle your co-workers when they don't invite you?

So via Facebook, I found out that there was a Christmas Party from my job, and I didn't find out until everyone from work started posting about how they had a good time and everybody will have a hangover at work. Well I never got the invite, if anybody asks me, I was thinking of responding with the most sarcastic nice voice that I wasn't invited and that's why I wasn't there. But then I feel that is too childish and although I do work with a lot of people who are childish, it won't get me anywhere. So what should I do? Smile to these peoples faces and show them that it never got to me, or make it known that it pissed me off that I wasn't told about this let alone invited. I have work tomorrow night and I'll be the first to admit that I can be a little bit of a hot head when it comes to being left out or not invited to things. Maybe because I'm so mad right now and can't sleep that this is why I feel this way. Anyways, I really would appreciate it if I could get a decent mature answer. I really do want to know how to handle this the best way possible because I'm starting to think that the people I work with just smile to my face and talk **** about me when I'm not around.