Thank you all - I knew that there must be several examples of "insider" usage out there, and the ones you have provided are very useful. Xara, if I find myself 15 younger and attending high school in Mountain City(?)Tennessee, I shall be sure to say "Prom" in order to fit in. Shanks, if I ever find myself in London, (only marginally less unlikely), I shall scrupulously avoid referring to the Tube lines by colour. The only one I can't use is "up to London", as everybody knows that North is down!