Ahhhhh, Portal 2. I shall name its release date "Semi-National Portal" day, which will probably be observed by well over half the gaming populace.
Traditions include massing food in the gaming room, locking one's self in, not coming out for several hours, calling out of work, playing hooky from school, and last but not least, annihilating all forms out outside communication...Unless its over steam, Xbox Live, or the Playstation Network for the sake of finding a partner to do co-op with.