It's a classic AMOG move people try on me. I shave it, rarely wear a hat so it's not an issue, I'm just unsure of a good response to it? Any pointers?

Earlier today someone did it to me in front of a group of people and I just stayed silent and didn't respond, let the attention focus on me, then poked him in the belly (he was a bit chubby) and went "he-he!" and everyone laughed and we moved on.