nothing
A craze that went on for far too long was getting urgently catching someone's attention, then saying "nothing" as though they were cretins for asking. It went a little something like this: "Hey John! John!" "Yes, Tuppence?" "Nothing" (cue laughter)
written by Tu*pence*, approved by Log
Another variant is the slightly more sophisticated "Can I just interrupt you there?" and when they say "Yes" you say "Thanks", and walk off. This is slightly irritating, however, to people who heard Saturday Night Fry on Radio 4 in 1988, formed a strong bond with the programme, only to hear other people you had lent the tape to saying lines from it and passing it off as their own. I went up to them, and said "your behaviour is like a bad underpant - transparent and unclean."
written by Jo* Bly*h, approved by Log