Pretending to wank followed by flicking the wrist, and the imaginary ejaculate, to one side. As you do this, say "oops!", as though ejaculating is the last thing on your mind when you're having a wank. The first time the "oops" variant was used was in a PE lesson. The bollockings and detentions lent it such bonus kudos that it caught on very quickly.
approved Nov 24 2002, submitted Nov 24 2002 by Daniel Buchan