Cthulhu Day, otherwise known as Chef Boyardee Appreciation Day, is the day where all of us petty three dimensional mortals worship our Dread Father. It is held thrice every year, on April 2nd, February 27 and December 2nd.
Cthulhu Day was set on April 2nd because that was the last time that Cthulhu rose from the depths to inhabit the parts we ground-walkers call ‘Home’. Before then, it was celebrated several days in advance, and most celebrations consisted of only nude dancing around the fire, and being captured by the police. Those celebrations were serving to try and raise Dead Cthulhu from his cyclopean house at R’lyeh, where he lay dreaming. They were afraid, due to the ‘Strange Aeons’ that were experienced that year, that even death may die. Well, their prayers seemed to have worked, because soon, Cthulhu rose to the surface, (although there is some dispute as to whether or not it was the prayers, or some bungling Norwegian fisherman, who actually rose Him.) only to sink back down beneath the waves and darkness of the opaque ocean.
“… And thus, on the Day of Insanity, when the stars are right, and the Earth is prepared for the infinite horror and madness that is hidden beneath the sea, Cthulhu will, once again, rise from his ancient temple at R’lyeh and, if He sees His shadow, the whole world will shout and kill and revel in joy and there will be 6 more weeks of winter.” – Necronomicon
(Info obtained from http://uncyclopedia.wikia.com/wiki/Cthulhu_Day)