I don't know how many ppl know about 'yolo' but it a motto used by the current generation of HS students. It means 'You Only Live Once' and they use it as an excuse to do stupid, crazy stuff or as a joke -mostly on twitter. For example "sledding behind a truck down main street with 4 other people. #yolo" or "didn't use the wii-mote saftey strap. #yolo"
Anyway Saturday Night Live did a music video about YOLO only they took it to the exact opposite direction. It's awesome:
The Lonely Island - YOLO (feat. Adam Levine & Kendrick Lamar) - YouTube