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When something is incredibly unbelievable.
It is the ugly cousin of the word unbelievable. Typically used when a person is angry or in shock.
John: "What are you saying, she not only ate the 18 ounce steak, but the 3 baked potatoes as well?"
Jess: "Yeah, it was unfuckingbelieveable!"
by mistressJessFantastic January 10, 2009
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