"Though I do think I know your intent (and probably agree with you in your intent), I can't help but ask: If he were to have written "and boys" after his comment, would you have responded the same?"
No, I would not have responded at all. To call on a bunch of men about a behavior or an attitude that needs some kind of straightening out, by calling them "girls" is worth noticing. Not every time something like this happens, is there an ill intent, but it perpetuates attitudes that would be best left behind . Phrases like that are so common that the majority of men don't even think twice about it, and they mostly mean no harm. That does not mean that no harm can come from it. Our kids watch and listen and it would be better if they did not hear us put down people by calling them "girls". Best if they did not hear us put people down, period, but that is a different discussion.
All I am saying is "hey, that kind of talk is not cool". And no, this is not my household, and neither is it the household where that kind of talk goes unnoticed.
A hat with a peace sign would be cool. I can do that, if you were serious about it.