This slang word is used to describe someone or something that is really crazy. It is just another way to say "crazy" and is widely used by the younger generation. This expression has been around for about 10 years and but it really became popular when the rapper Jay-Z used it in one of his songs.
I have so much work to do today. I think I am going to go cray cray.
My brother met this girl recently. She keeps texting him and calling him all the time. She keeps asking him to go out on a date even though he clearly told her that he is not interested in her. I think she is really cray cray.
Tom: Hey John, can I borrow your new car? I want to go to this cool party tonight.
John: Oh ya? Are you a good driver? How long have you been driving?
Tom: Of course, I am a good driver. I mean I failed my driving test 2 times, but I passed it the third time. And I have gotten in an accident only once this year.
John: Dude! You must be cray cray if you think I am going to lend you my car.