I've gotten this before because I am "just a teacher." I'm quite certain that most adults could not survive a day in a middle school! I've learned to just roll with it and say something sarcastic or witty. My son's older now and he thinks it's funny so when people ask him how he got so smart he'll say "Zeus is my real father." That always makes me laugh... though it does make some adults walk away with puzzled looks!
I tend to go with, "I've asked myself that many times," but I've also said "Genetics". "He's not mine, I'm just his nanny," my favorite line when I don't know the person and don't care what they think!
