Frank,
I would explain: "In some circumstances, a PA or NP can be just as good. There are other times where the difference can be critical. There are times when a lunch at your local sandwich shop is just fine. On the other hand, there are times where you want to eat a meal like the one we were kind enough to have just served you, and I would imagine that you can see the difference."
In the spirit of Christmas, invite him back for dinner next year, but instead of 100 year old Gran Marnier, serve lukewarm diet Coke. If he has the nerve to complain, explain that in some cases it is "just as good".
I like this idea, but variation on a theme. What's the worst possible alcohol you have in your house? Ask them to suspend drinking the Grand Marnier and try some of this. Then explain that for some things "good enough" will do, for others, you may need "finesse."
People are entitled to their opinions, sometimes it is not worth the effort to try to explain. They may be looking for a fight.
I am slightly unsure who made the comment, the friend who self invited or the friend of the friend. (I am assuming the latter, but really doesn't matter.) In either case, I would simply not invite either person next year. If friend shows up, simply state that you will sponsor them to a Subway dinner since it is good enough.
