1 definition by a sensible person
Rainbow formal is a dress code similar to black tie, where the attendees to the event (normally a ball or awards ceremony) are required to not wear the usual white shirt, with black tie, jacket and trousers and instead dress like a idiot in their stupid coloured jackets and shirts, while still trying to stop people turning up in jeans and a t shirt, or anything that doesn't look stupid.
"we organised an event and eschewed the usual black tie, instead choosing to dress like a bunch of tosspots in 'rainbow formal', while remaining smug and snobby by avoiding casual dress."
by a sensible person March 21, 2007