2. Synonymous for masturbation
There is a new device with Pokemon Heart Gold/Soul Silver that lets you take your Pokemon with you walking, known as the Pokewalker. It features a lot of Pokemon not found within the games themselves that you can catch, but you have to walk a lot in order to unlock some of the locations. In order to cheat the system, i.e. not walk every where, you have to simulate the walking motion with an analogous motion. Some people hold it in their hand and move their hands up and down in a straight motion, which if observed without noticing the Pokewalker in one's hand, looks quite a bit like a hand gesture for masturbation.