I didn't realize people thought it was an acceptable answer, I just thought it was something people said afterwards (as in, "Can you believe he asked me about the fourth argument to the foo function? In real life I'd have just Googled it"). It's almost an insult to the interviewer (Of course I don't know the answer, you shouldn't have expected me to).

As an aside, I hope people don't mean this literally. If I wanted to know what the fourth parameter to function foo is, I have quick access to my language's reference manual, and I look in there. I don't just pop it into Google and hope whatever comes up is right.