The dolphin switch is a metaphorical "switch" that can be flicked when one wishes to change their sexuality at the drop of a hat.
Born of the concept that Dolphins can "switch" between safe sex and unprotected sex whenever they so wish - so why wouldn't they be able to switch sexualities?
Aww man...that guy's so hot....but I'm dating Amanda!" "Dude...just flick the Dolphin Switch!" "Aww man, didn't think of that. Click. Done!