The Downer – This is the person that needs to explain their problems or current state of woe to as many people as possible, and becomes antithetical to any kind of celebratory mood. Parties, and most social gatherings, even wakes (especially involving someone of Irish descent), are an escape from the humdrum of everyday life. These people can dampen your party.
What else you might try – If this person exhibits this behavior consistently, try not to invite them. Otherwise, try to maneuver them into a small space or a corner where they can do much less harm.