Is this annoying yet? How about now?

Every time my son says "Guess what" to me (which, if you've ever been around a four year old you'll know is quite often) I answer "Chicken butt". Then he says no, and proceeds to tell me what the guess what was about.

So far he hasn't shown annoyance, just calmly says no as if I was seriously suggesting that chicken butts were worth a big "Guess what!". I'm going to say it every time until he finally gets irritated. But I'm very curious as to how long this will take. Any guesses? How long would it take to annoy YOU?