In the car last night, Babs said something fairly rude to the Boy. While the parents and Babs tried to settle whether she knew how rude she was, why she should have not said that and the like, he continued to babble and sing happily in his seat, obviously not bothered at all.
But we were bothered (and Babs was too, I don't think she realized how much we would not approve), so I told her to at least apologize. She got an "I'm sorry" out through her tears.
Despite his own conversation, the boy was obviously paying attention, because the minute she choked out her apology he yelled "BIG GIRL VOICE!" repeating a common refrain around the house, "stop talking like a baby and use your big girl/big boy voice."
Luckily it was dark, and the children couldn't see the parents almost cracking up in the front seat from his reply. We explained that she had used her big girl voice and tried to move on.