My step-dad is an avid Pepsi fan and I used to only drink Coke... so naturally I taught my sister when she was little to say "Coke is good; Pepsi sucks!" much to my mom's disapproval. Anyway, when she was maybe 4 or 5, she said that once, and my step-dad retorted with "Coke sucks!" My little 4-or-5-year-old sister quickly turned on him, stomped her foot, and screamed "YOU suck, Daddy!"
There was a slight pause before both he and I burst into laughter. I was quite proud.