A pairing of two words, Insane and Crazy.
This conjunction is used to define an extra specially Insane/Crazy moment or object.
Made famous by Tim Westwood in 2005 on the UK version of Pimp My Ride.
The term may also be heard in the slighty different variation of Crazy Insane, but both versions mean the same thing.
Me: Hey! look at those wheels!..
John: Man that is insane crazy!