How do you translate the English phrase "Is this guy for real?" into its Japanese counterpart? The statement is uttered in a tone of disbelief. And preferably in an informal and colloquial setting, like the conversation between two friends, etc.
would be the best equivalent I could think of.
I, however, would strongly suggest that you not use it unless you are already fairly fluent in informal Japanese. Nothing sounds "funnier" and out of place than a slangy expression thrown in amidst an unnatural-sounding textbook kind of speech.