So here's a question to all those who think the workplace have been mean to the OP - is every little oversight or thoughtless act in life a sign of people being deliberately mean?
I just think life and people's motives in life are a bit less black and white. Often things happen for a variety of reasons and not just because people set out to be 'good' or 'bad' and a problem arises when people interpret everything in light of people either being for or against them.....when in actual fact, quite often the things that had nothing to do with anyone having any thoughts about you,either positive or negative. It's actually quite egotistical to imagine that very thing that happens is because people are dedicating lots of thought to you and could even be bothered to dream up ways to be mean.
And in this instance, the problem is likely to be simply that people did t think enough. I sure the office didn't sit down when drawing up the list and say 'we don't like X.....lets invite every single other person and not her' - to imagine something like this is daft.
Probably someone organised it months ago before OP was there. Yes, as time has passed and the event got closer, no-ome thought to say 'and what about X - she's not on the list or has joined since we planned this' simply because they are busy and lots of our things filled their heads, or because everyone simply assumed someone else would have thought of it. It's not mean behaviour, but very usual behaviour in a largeish office, which if a little thoughtless, couldn't be said to be worse than this.
Perhaps I'm a bit more thick skinned than OP, but if this happened to me I'd just think 'oh shame, but I can see how that happened' and I would say something lightheartedly about it, absolutely expecting it to turn out to be an oversight not an exclusion. Of course,mid it did turn out to be a deliberate exclusion, I would be shocked.....but to be honest, apart from groups of early teenage girls, I've never known adults in a mature workplace to invite absolutely all workers and volunteers to a do and then to deliberately exclude just one person - which is why I think it's unlikely.
OP though has a bit of a sneaking suspicion that this is what happened, or that the fact she was overlooked means she isn't cared about enough. If you are feeling a bit sensitive or your self esteem isn't at its peak, I can see his might be an immediate feeling, but I hope that lots of really sensible posts on this thread (alongside the ones that feed the OPs anxieties that people were mean to her) make her realise it's very likely not to be personal and she's overthinking it, and that she probably ought to raise the party with someone for her own peace of mind, if this is goi g to niggle her.
Again, not good to approach from sounding hurt or angry or using the word excluded. Much more useful to just observe lightly that you know the party happened and simply wasn't aware of it 'did I miss an email?' type comment. And whatever info is then given, a cheery 'it looked fun, hopefully I'll be able to join you all next year' is a good reply.
Of course might turn out it was a smaller group or individuals who organised something and not a big official do for everyone - not always easy to tell on Facebook....and it won't be the first time seeing pics on Facebook has made someone feel they have been excluded.