This word is used when the thing or person is so incredible that they or it exceeds the word incredible to the point were you are forced to inject the word "FUCK", hense In-fuckin-credible.
Damn that car is In-fuckin-credible; Shit Christian was In-fuckin-credible last night; I had an In-fuckin-credible evening.
by Christian Champ June 17, 2006
Get the In-fuckin-crediblemug.