Gaudily-dressed 30s comic Max Miller reputedly had two notebooks, a white notebook for 'clean' humour, and a blue one for 'adult' jokes. It is said he would ask his audience at the start of a gig which book they wanted to hear stories from. If they chose the blue book, it was their own choice and he could feel reasonably secure he was not offending anyone.
Follow Up Joke:
A woman walks into a bar and asks for a double entendre. So the barman gave her one.
Then a sound engineer came in and gave her one too, one too.
