Ugh! Time for scowling lessons?

I got a rare glimpse yesterday into the minds of Matthew and Jonathan and how they experience the world as identical twins.
We were sitting in the minivan after a school field trip, waiting for their older brother and sister to emerge from the building.
A friend passed by with her twin boys, who are two years younger than our guys.
I opened the sliding van door so Matthew and Jonathan could see the other twins and say, "Hello."
My friend's twins both have the same hue of bright blond hair, the same fair skin and are about the same height.
But one of her boys has curls and an outgoing, social personality.
The other has straighter hair and is more clingy, more cautious in his approach.
Though they are obviously brothers, I've never had trouble telling them apart.
They are clearly fraternal.
After the other twins left, a conversation ensued in the back seat.
Jonathan: "I can't tell them apart. That's why I don't use their names."
Matthew: "Yes, they look the same to me."
Jonathan: "At least they weren't dressed the same. That helps."
Matthew: "I think one has a fuller face. I still can't tell them apart though."
I was stunned.
I wasn't sure whether to laugh or cry.
How many times had they heard this?
How many people have examined Jonathan and Matthew and spoken of them -- right in front of them -- as if they were simply objects, highly insensitive with their games of " What makes these pictures different?" This back-seat conversation was clearly not about the twin friends we'd just seen.
Matthew and Jonathan were emulating adult conversations, conversations they'd overheard.
This happened frequently when they were babies and toddlers.
I didn't worry then because I figured Matthew and Jonathan couldn't comprehend it anyway. They were immersed in their own, egocentric worlds. But as they got older, I started to hush people when the comparisons began.
Then, when they got a lot older, I started to scowl.
Soon it seemed that people had gotten smarter.
They still compared the boys. That's only natural.
Heck, I do it too.
But they compared them out of earshot.
I guess the reactions to my scowls misled me.
I'd thought things had gotten better recently, that the overt and callus comparisons had become less frequent, especially since Matthew and Jonathan rarely even wear the same shirts, have tried to achieve different haircuts, have developed such different personalities, and have different amounts of fullness in their faces making their expressions unique.
I guess I was wrong.
Jonathan and Matthew are out of my hands more often nowadays.
They are in preschool four days a week, where they interact not only with teachers, but with parents of other children. Teachers tend to be sensitive, but that doesn't ensure that other adults they encounter will be.
Sigh.
I've taught Jonathan and Matthew to be upfront when people are unsure who is who and tell them their names. Right now, they aren't bothered by that. I've tried to help them understand that it's not an insult. People just need help sometimes because they look so much alike on the outside.
I guess we need another lesson though.
I guess I need to teach them how to scowl.