Wimp. If the men had not taken off their hats, or it was OK to wear them indoors, that would be one thing. But heck they knew they'd messed up. Why be embarassed that your Dad, bless his soul, pointed it out to them. An old guy can get away with stuff like that. :)
Hats indoors is a pet peeve of mine too. I don't see it much around here, but then I work on the largest military base in the free world. :) They don't go into a Blimpies and not take off their cover as they go through the door.
I used to eat in a restaurant that had a sign “If you wear your hat at the dinner table at home, please do so here. We want you to feel at home”.