A male whom when using a public restroom switches from the urinal to toilet midstream. Said person may still be considered a switcher if he switches during one go. They're commonly found in bars where you will usually find a urinal and toilet within close proximity. Alcohol is almost always involved and fuels a switchers switching.
There have been a few reported cases of female switchers, but at this time they're considered a fables.
You walk into a bar's restroom to go to the bathroom. A male is standing at the urinal. You look away and when you look back they're on a toilet. This is a switcher.