Which of the following correctly describes the reason for including a dress code with an invitation?
-- To sharpen your rapier wit on your would-be guests.
-- To inspire your friends to reach new heights of sartorial creativity, challenging them to think "outside the box." (Inside the box there is now so much unclaimed real estate that those of us still in residence are not coming out, barring actual flooding.)
-- To sow confusion.
If you chose any or all of the above, you may join the majority of your fellow citizens who celebrate their individuality by conforming as strictly as possible to the prejudices of their peers. It is more crowded in this box than Miss Manners had thought.
The purpose of a dress code is to save your guests from having to guess what is expected, while comforting them that if they wear what is asked, they will not spend the evening dodging dirty looks from a partner -- or having to regale friends with the hilarious story of how their ties got caught in the car door.
Miss Manners would have thought this would be appreciated by the perpetually overbooked and uncomfortable Modern Lady and Gentleman.
Such is not the case.
Miss Manners does realize that some of the more fanciful dress codes are intended to be humorous and playful, but there are places where humor does not belong. Fire exit signs and confessions that you wrecked your parents' car come to mind.
A proper dress code should be understandable to its intended audience. Once upon a time, it was understood that "formal" meant white tie, "informal" meant black tie, and the absence of a direction was what some now term "business attire." Decades of improvisation have destroyed that understanding, relegating such terms to the waste bin of useless words, where they sit next to "semiformal" and "inflammable," awaiting a final disposal that never comes.
"Black tie," "jacket and tie," and, in the case of public accommodations, "no flip-flops" lack joie de vivre, but they make up for it in intelligibility.
Notice that most dress codes specify what is expected of the gentleman, rather than the lady. One would think husbands would be used to this by now, but the reason for it is practical. Male clothing, particularly as it increases in formality, is more prescribed than female clothing. Who, other than the owner, can say which is a lady's second-best dress?
If all this is too much for you when issuing invitations, there is no requirement to specify a dress code at all. The smart (though confused) guest will call and ask, and you may then discuss it at as great length as you feel up to. At least it will take less time than trying to parse the differences between "cocktail attire," "smart casual," "tea party dress," "country club wear" and "after-5 attire."
As for "business casual," Miss Manners suspects that it is not a dress code at all, but an accounting practice, accessorized with handcuffs and subpoenas.