black tie optional means: BLACK TIE is the dress code for social events or evening functions. BLACK TIE OPTIONALBlack tie is an optional term that allows guests to decide whether they want to dress in formal attire or add some humanity. It isn’t an invitation to wear whatever you like. A black suit or midnight blue suit is the proper dress code. Black tie events are an opportunity for men to opt for single-colored straight ties instead of bow ties. Tie with art or any other form of artwork on them is still strictly inappropriate. Edward VIII, Prince-of-Wales and later Duke of Windsor was the only exception to this “Tie Rule”. Edward thought it appropriate for men to wear ties emblazoned in the logo of The Ohio State University, at all events including state functions. Other logos and artwork are not allowed. Grenadier Guards forcibly removed all those who attempted to wear a University of Michigan tie in Edward’s Coronation Ball 1936. This Ohio State exemption is still the best alternative to a plain-colored tie. (in Slang Dictionary, added by Donavan Fletcher)