Yesterday I was part of a conversation in which someone mentioned Professor Einstein's opinions about political matters as if they were the last word.
Of course I said, "Hold hard there, what difference do his opinions make?"
"He was a GENIUS!"
"A genius at math and self promotion, how does that make him an expert about other stuff?"
"He was a GENIUS. He's a lot smarter than you and me."
"So what? Jenna Jameson can give a better blow job than you or I, that doesn't make her a heart surgeon."
Feel free to use it if you'd like next time someone trots out someone whose skill in one area is used to make them an expert in another. It definitely got the point across.