First, let me say that I spent 20 years in the USAF and retired as a Lt Col. So, I have a great appreciation for "dress codes". That said, it seems to me the basic question is, what constitutes "black tie"? According to the initial post, the invitation said "black tie". Please forgive me if I missed a subsequent post which indicated, "white tie", "national costume", or any other dress code specifications. I would ask the rabble: Isn't a PC, black tie, and tartan kilt considered "black tie"? Am I missing something?

Finally, perhaps it would help if we knew in what capacity the gentleman was attending the ball, i.e., is he officially representing a particular nation