Where are our manners?

I presided for the first time at a Women’s Club meeting and a few of the girls (I’ll call us girls even though we’re all over 50) had to leave early. We hurried to address business that pertained to those leaving. As the first to depart rose to go, I said automatically, and half jokingly, “You may be excused.”
It felt familiar saying it, but I couldn’t place what had struck me about the phrase