A more "embellished" phrase of the classic saying "Holy shit"!
An example of when to use it would be after excessive amounts of exertion to illustrate the mixture of exhaustion and lack of giving a crap about whats coming out of your mouth.
1) "Holy christ on a crotch! You almost got pancaked by that car!"
2) "Holy Christ on a Crotch, 'huff', thats a lotta stairs!"
Invited by a user on a popular video sharing site, it describes people who dye their hair blue. It's similar to how people call redheads "fire crotches." Color of water = blue. Color of blue haired girls crotches = blue.