Grass orgy
The original grass orgies were somewhat innocent ha-ha-game-style piles of CTY-ers. But in recent years, at least at Siena, grass orgies have grown to include any activity in which several CTY-ers are in a pile on the grass.
When I was at Siena in 2002, a grass orgy meant rolling around in the grass entangled with as many people as possible, and making it look like everyone was making out with each other. Most of the time, no actually making out occured.
My friends and I are fairly certain we invented the term "grass orgy" at Siena in 2002. It was mostly a joke, where we'd roll around pretending to be romantically entangled. However, this year (2006) Siena has instituted a "no lying on the grass" rule, thus putting an end to grass orgies.
A grorgy in action, LAN.05.2: http://tinypic.com/ifztxj.jpg