If you're looking for an excuse to spend more time with friends, all the while looking busy making something - consider knocking up a version of beer Pong as described by Instructables user "PotNoodle". It's quite easy - using piezo sensors under each cup with an LED next to the sensor, the game detects when a cup (or skittle, etc) has been knocked over and lights the LED. Furthermore the Arduino can generate various sound effects as well. It's a simple project that's open for experimentation, and can be a lot of fun after a few drinks:
If you're interested in working with piezos for various reasons we have a neat little SOUND: sound and buzzer module:
It can be used as a noise-maker driven by your microcontroller for audible feedback of events, and it can also be used as a knock-detector input to sense events and react to them. Includes a built-in 1M resistor to allow the piezo element to detect shocks. For more information and to order, please visit the product page here.