It would be ok.

I dunno what a Christmas do is, but it sounds like a Christmas party? If so then yeah I'd probably still go, provided there are other people going that I actually like. Maybe i'll discover that this one person isn't so bad.... and if not then i love a good story

yup, just don't talk to them. bad people shouldn't stop a good time.

Probably.

... when that person was an ex and we had some fresh fallout of the split then likely yes.