According to The Cassell Dictionary of Slang and I quote "The OED's first citation is from a letter by the actor David Garrick (11th July 1741): 'I am far from being quite well, tho not troubled with ye Blews as I have been.'" Unquote. So tomorrow July 11th is an anniversary of sorts. Obviously the word must have been in use before that in order for Garrick and the person he was writing to, to be familiar with it. As Garrick was an actor I wonder if it had a theatre connection?