One particular incident comes to my mind.

I was talking with our son's preschool teacher about something he had done that day. She said I must be a very good teacher (because of whatever it was he had done).

I simply said that he was easy to teach. It's the truth and how can anyone challenge that? I'm not about to elaborate with a stranger (yes, preschool teacher is a stranger, imo) that he only needs a couple of repetitions and he has whatever down.

I've also said to other comments about how much he knows: "He's a busy boy". Usually I move on and don't give them a chance to question me further.