Is stop talking crazy an idiom?

"Stop talking crazy" isn't a recognized idiom. It's a straightforward phrase used to tell someone to stop saying things that are illogical, nonsensical, or unbelievable.

However, it's close to the idiom "Stop talking nonsense." This idiom is used to tell someone to stop talking about things that are ridiculous or untrue.

So, while "stop talking crazy" is a common phrase, it's not an official idiom.