"You gotta be joking me" is fine to use in conversation considering the casual & informal nature of the phrase. The use of "joking" instead of "kidding" here makes the phrase sound funnier and has a more aloof, goofy tone, which is the reason it's used.

P.S. To the more die-hard prescriptive commenters in this thread... it's really strange to be so @nal about this type of colloquial speech. This is not an essay, this is not a law, this is not a scientific report; this is banter with friends. Dancing around the rules of book grammar in these types of conversations is perfectly reasonable!