Checkout Lines

So a dear friend of mine who has a daughter with Autism reminded me of something today. We were discussing on a thread how sometimes you are forced to explain your situation because of how your child is acting. You don't want people to think your child is being rude. The scenario she brought up which stuck out to me is in the checkout lines at the store. The people are always trying to talk to/give treats/stickers to Michael. He doesn't take well to direct questions like that so he's always saying "NO WAY!!!" or something similar to them. I know they are just trying to be friendly and they don't understand why my kid is yelling at them. I hate that they may think he's being rude, because he doesn't understand that concept. I normally don't explain the situation, I just smile and say something to Michael to calm him down but I always leave feeling a little bit upset over the whole situation.