I don't think knighthood is technically a "title of nobility" as mentioned in the Constitution.

For one thing, it's not hereditary.

It's just an honor. There's some polite thing U.S. citizens do to say, 'thanks a lot, but I won't actually be using the title'. I used to know what it was but I've forgotten.

I thought we fought a war over this kind of thing. American government officials receiving foreign titles? Hm.