A sarcastic adjective used to describe an occurance or act that is unwelcome and/or troublesome, and is the direct result of someone doing something so unbelievably stupid as to suggest developmental disablement. A portmanteau of "retard" and "terrific".
Jimmy: "Al just split his head open tryin' to ride his bike off the roof and into the pool."
Dad: "Well isn't that just fucking tardrific."
The state of being afflicted with severe, chronic redonkulousness.
Boss: "Jimmy, I need you to get naked, take this handful of dog shit, and smear it on that beehive."
Jimmy: "You must have a bad case of Redonkulosis if you think I'm fucking doing any of that."