G_razy is a combination of great and crazy. This combination of words express a superior delight not able to be expressed previously through the words greatand crazy alone.
Also, though rarely done, the word G_razy could be changed to mean im as crazy as a G, or a gangster in other words. This way you could mean many things at once giving you again a greater power to express feelings.
*Being interviewed for a job
Boss- Hello Mr. Williams. How are you doing this fine afternoon?
Random guy named Mr. Williams- Im G_razy
Boss- Wow with that interesting word you have really impressed me... You're hired!!!