A religion that includes all possible deities (i.e. the flying spaghetti monster,thor, zeus, yahweh, ganesha) and the events that are influenced by them. It explains the universe's beginning as a quarrel between all of the gods because of ganesha's superior size. The great spirit mistakingly decreases his volume and creates a black hole. This focuses all of the particles that made up the deities into one point which causes the big bang.
P.S. Omnitheism is a religion created to display the fault in shunning all possible other gods. Mneurgh.