To perform an act in an opposite manner to that in which you would normally perform it.
Originally used in skate and snowboarding parlance, but now adopted into wider slang usage.
Can also refer to partaking in anal sex with a female.
Orig. - Man, that was sick when you landed that 540 and rode it switch!
Now - I normally sit on the left side of the couch, but I thought I'd go switch,
Vulg. - Debbie was on her rag so I rode her switch instead.