As, I think, would many of my dashing flisties.
Watching the English: The Hidden Rules of English Behaviour
It's hilarious. Useful for UK-based fanfic (coughHarryPottercough) and also just an outright string of laughs - to be expected from a culture so deeply saturated with humour (imbibed as often as rain). It's made me laugh out loud more times than I can count. A thoroughly enjoyable book.