All that practice came in handy eventually...
Walking through the coffeeshop back from lunch now, did the classic double-take look (thanks for the training, Tom!) as I spotted one of my ex-student colleagues at Sussex in a suit talking to a bunch of librarians. I had heard that he had gone into publishing though, so not that much of a shock really. As he seemed to be in the middle of an earnest discussion I didn't interrupt (plus I doubt he'd recognise me anyway these days).