Don't use the party as a time to gossip about co-workers or anyone else.  Gossip is a bad thing anytime and I don't want to be anywhere near it.  If someone does start to jibber-jabber about others, my advice is to move on.  If you have to, change tables.  

 This can never be a good thing and can only do harm.  Stay positive and friendly and use the time to try to learn things about co-workers that you don't already know.  Engage in conversation with folks you rarely talk to.  You never know what you'll learn.