This includes wanting all Christmas cards to say "Season's Greetings", not "Merry Christmas" and berating people for using the word "black" even in the context of describing the colour of a dinner suit.
The rainbow sheep might claim to be a human rights activist, but usually they are just seen as a party-pooper.
Rainbow sheep are usually white and middle or upper-class, but are often unable to admit this.
According to Freudian psychology, the Rainbow Sheep is using a defence mechanism called Reaction Formation. This means that they actually have unconscious racist/sexist/non-PC views which they fear, so they make sure that their outward behaviour is the exact opposite to what they really think.
This term was coined upon hearing that schoolchildren were being taught to sing "baa baa, rainbow sheep" instead of the traditional nursery rhyme, "baa baa, black sheep".
"oh, don't be such a rainbow sheep".
"He accused me of being sexist when I asked if the milkman had been round. He told me I should say 'milkperson' instead. What a rainbow sheep".