I suspect most of us attend few black tie affairs and probably have never attended a white tie event. Consequently, when the opportunity for fancy dress arises there is the urge to "dress to the nines" as Downunder Kilt suggested.

When living in California in the early 80s it was not uncommon to see a Montrose or similar jacket, jabot and laced cuffs, and the fly plaid to Scottish country dancing Balls. The men wanted to dress up in all their Scottish regalia and these were the only opportunities to do so. More recently I've seen much the same trend with of wearing of a fly plaid and buckled shoes with a PC or Argyll to a black tie affair.

Is this appropriate attire for the occasion? No. But no one was going to object because either they don't know the customary criteria regarding white and black tie attire, or more likely because we enjoy seeing the full regalia being worn.

Perhaps we are "guilding the lily" a bit, but consider the alternatives. I've seen blue jeans (denims) worn with a tux jacket to a black tie affair so I wouldn't be too surprised someday to see someone where soemthing like a ghillie shirt with their PC.