MoogMod39,963 Locked 27 Apr 2011 03 Jul 2011
This achievement is self explanatory. Play and complete a game on July 4th and the achievement will unlock. A turncoat is someone who deserts one party or cause in order to join an opposing one. Since You Don't Know Jack has always been American based, the achievement is saying you're a turncoat for not celebrating Independence Day, an American holiday that celebrates the adoption of the Declaration of the Independence which declared independence from Great Britain back on July 4, 1776.
If you're impatient and can't wait for July 4th to roll around, you can get this achievement offline. Make sure you're not connected to Xbox Live as when you're connected to Live, the time on your Xbox has to be the same as Live's official servers. Then, when you turn on your Xbox press the Xbox Guide button: Settings tab -> System Settings -> Console Settings -> Clock -> Date and Time and then set the day for July 4 and confirm. Load You Don't Know Jack while still not connected to Live and complete a game and the achievement shall unlock.