Origins: the adjective root, ridonkulous, evolved from the ithyphallic wordplay of replacing the "dic{k}" sound in ri·dic·u·lous with "dong" (the "g" becoming silent). The spelling of the root using a "k" instead of a "c" results from the common misconception that the word donkey is somehow related.
An amazingly awesome fluke or mishappening that only occurs when something that has never happened before. An end result of a chain of outlandish events that lead up to an almost inconceivable out come. Can also be an inevitable failure turned into an sweet presentation of unknown skill. Accidental awesomenicity.
When you drop something but make an attempt to catch it and fail but hit it high enough to make another attempt and another and another and another until you finally grasp it and you look up and everybody cheers, and their only possible response is "That was ridunkulous"