This @ the language log is hilarious
Adrian Morgan pointed out to me a Usenet comment in which someone says of some course of action that it “can hardly be a sane policy for anyone who is not evincing signs of heading distinctly dagenham”. In this context dagenham is apparently to be taken as a synonym for “insane”, by a rather devious etymological route. Dagenham is a town in Essex, England. On the District Line of the London Underground, Dagenham is three stops beyond the town of Barking (after Barking are Upney, Becontree, Dagenham Heathway, and Dagenham East). To be barking mad is to be crazy; and being dagenham is therefore being three steps beyond barking.