Embarrassment...My son has finally reached the age where he's starting to say things that embarrass me in public. Anyone have any advice on how we're supposed to react to these situations?

In the grocery store, Hayden sees a man with about half his face covered in a large dark birth mark.
Hayden (loud and clear): Mommy, what does that man have on his face?
Me: A birth mark, kind of like the mole I have on my arm. But it isn't nice to shout out when somebody looks different from us.

In Nordstrom, after almost running into a man while acting wild in the store:
Me: Hayden, be careful.
Hayden: Why, because I almost knocked over that OLD man?
Man (about 45 I'd guess): I'm not THAT old!
Me (sheepishly): Sorry.

In the bathroom at the movie theater:
Me: Wash your hands.
Hayden swipes his hands under the water
Me: You need to use soap Hayden
Hayden (loud): But that lady didn't use soap Mommy, she just ran her hands under the water.
Me: You just take care of yourself and never mind what anyone else is doing.

It's obvious we must be due for some long talk about manners, but I'm not sure it would even make a difference. He's just at that curious, running-commentary-on-everything-I-see stage. So I'm not sure I can really reign him in, so if you see us on the street, run and hide or my son be sure to point out your most embarrassing feature.