Not half bad

If you want to check the class status of a new acquaintance (and which English person doesn't, if a trifle guiltily, want to do this?) I offer a simple test. Tell them a friend saw a film/watched a play/read a book and told you it "wasn't half bad." Ask them how your friend rated the experience.

Middle-class folk, as well as most Yanks, will tell you your friend thought the film/play/book was pretty good. Working class people will understand that it was worse than bad, it was execrable ;   the same interpretation will be put forward by those of working class origin who are merely pretending to be middle class.