I am Bipolar and it can be a very destructive illness.
I have found that I have lost many 'friends' over the years, these were the people who pussy footed around me, treating me like I was fragile - they over-reacted to anything that I said (the stupid throwaway comments that we all make) and any relationship will fail under such circumstances.
I now have friends who treat me as they would if I were not ill - they are sarcastic, they tell me jokes and funny stories - normal stuff. My brother and his family are good to me too - he refers to me as "crazy auntie Susan" .
Your son is ill and has been ill for some time - during this time he has worked and lived his life, he has interacted with you and his friends. He sounds like a survivor. So relax and treat him as normal - have a fun time at Christmas.
Try looking at this website to see if there is anything that might help you understand.
http://www.mdf.org.uk/?o=56878
Remember this is not the end of the world - give him the chance to talk but don't push things.
Have fun at Christmas.