Someone who destroys the life of a party, get-togethers or other social gatherings. This is done by being a bad sport, being in a bad mood and letting it be known, someone who thinks if they can not have a good time then no one else should, or someone who announces bad news about themselves at a joyful time and making it all about them.
"I can not believe what that guy did. Just as I was telling my friend that I got accepted into med school he came in and announced that his girl friend dumped him. He ruined my night. He's such a down dragger."