I went to Liverpool for a night at the theatre with some Rocky Horror friends a few years ago. There were a whole bunch of us in costume; walking up the road at three in the afternoon, we had coins thrown at us. The logic of this, if you could call it that, is 'what are those freaks doing? We must show our disapproval by throwing coins of a low value at them.' Coins, because being small and yet hard, they make excellent projectiles and hurt rather a lot when you get hit by them. Of course, this was infinitely preferable to being surrounded and physically pushed around, as happened later on that evening.
Ahh the old Liverpool throw coins thing... In Washington, DC the favorite of people was old batteries to throw at people... I remember that...