Most commonly recognized as an action performed on Facebook.com's "superpoke" application. Usually misinterpreted as a sexual activity, it actually means to throw something/one out of a window.
Steve - "Haha, check out my facebook, Kelsey defenestrated me. She must want me man."
Billy - "Dude, your a fucking retard. I'm going to show you what getting defenestrated really is."