Hacking.

OMGWTF people hack Team Fortress 2 (360 version, no less) like crazy. Why is this awesome?

• Upon entering a hacked game and spawning in one, you will likely be immediately destroyed by somebody on your own team. If you're lucky you will be able to escape.
• I escaped from our base, only to find myself face to face with a hunter gunship. From Half-Life 2.
• Moon gravity
• Getting the 'Grey Matter' (25 headshots as sniper) achievement is easy. Just snipe your teammates.
• As sniper, I found that the man in charge of the hack either did not like snipers, or was sincerely trying to find me a good sniping spot but failed, as I was being dragged all around the entire map with no control. It was pretty sick seeing the map in its entirety.
• Half-Life 2 rollermines floating in the air.
• A scout running around in the air...with the control point under him. It looked like a godly UFO.

And yes, I know that the possibilities on the PC version are five million times anything the 360 hacks can achieve, given the ease of hacking a PC game as compared to an XBOX, but still, it pretty much made my day.