Pulling your hand up and down like you do to get a truck driver to honk his horn at you has recently become an inside joke with a few of my friends :o

We were in a car, driving from you-don't-want-to-know to who-knows-where, passing through i-don't-care at just about this time, suffering from the general boredom that generally comes from this type of activity, so we started taking bets as to who could get the most people to honk at them. One of the people in the back seat started doing it way too far up and down, so that it looked like he was jacking off instead of trying to get a truck driver's attention (although it did get attention, that's another story entirely :p). Our collective minds all got the same impression from it, so we always do the truck driver horn thingy at him whenever we see him.