The ugly Christmas sweater party is one of the weirdest trends of the holiday season. In 2001, Jordan Birch and Chris Boyd threw the first official party in Vancouver, Canada. Their hope was to have the "cheesiest, most feel-good Christmas party ever." When photos from the event went viral, people starting throwing their own parties, encouraging friends to find the ugliest sweaters possible. Now, the parties are more popular than ever. Thrift stores are often cleaned out by December. A new book documents the trend: Rock Your Ugly Christmas Sweater, by Anne-Marie Blackman and Brian Clock Howard. Here are a few of our favorite looks from this collection of hilarious photos of people rocking their ugly Christmas sweaters with pride.