Someone who is a switch in bed, that is, someone who can be a Dom or Sub in bed depending on the situation, who also prefers to service their partner during sex. Focusing on their partners pleasure rather than their own, or taking pleasure in their partner's pleasure.
John's a Service Switch, he knows when to takecharge, when to lie back, and always knows how to make his partner feel good.
Playing switch or just switch is when you stick one thumb in your ass and one in your mouth and then switch. Often used as a pejorative to describe someone who is a major dumbass.
Q: Where's our idiot boss?
A: Oh, he's been in been in his office all day playing switch.