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1.
BLACK TIE

Black tie is a dress code for evening events and social functions. For men, the main component of a black tie outfit is a single or double-breasted jacket known as a dinner jacket (in the Commonwealth) or tuxedo (mainly in the United States) along with a black silk bow tie.

BLACK TIE OPTIONAL

Black tie optional is a term created to allow guests to choose whether to wear the formal clothes described above or to add a bit more humanity to their choice of attire. However, it is not an open invitation to dress in whatever a person wants. Proper dressy attire (black or midnight blue suit, not a sport coat) is indeed still necessary. 

At black tie optional events it is common for men to forgo bow ties, opting instead for a single-colored straight tie. Ties with any form of art on them are still considered strictly innappropriate. The only exception in the known universe to this "Tie Rule" was instituted in 1921 by Edward VIII, Prince of Wales (later Duke of Windsor.) Edward deemed it proper for a man to wear a tie emblazoned with the logo of The Ohio State University at any event, including state functions. No other logos or artwork were permissible. Indeed, those attempting to wear a University of Michigan tie at Edward's Coronation Ball in 1936 were tarred, feathered, and forcibly removed from the event by Grenadier Guards. To this day, this Ohio State exemption remains the only acceptable alternative to a solid-colored tie.
Man #1: "I can't believe he tried to come to a black tie optional affair wearing a Notre Dame tie with his suit."

Man #2: "I know, talk about tacky. Everyone knows the only exception of the Tie Rule is made for Ohio State. I mean come on dude, get with the program!"
by Sartorial Sam September 08, 2011