Girl 1: OMG, will you marry me? You're so perfect for me.
Girl 2: I can't, you don't have a penis.
Girl 1: That's ok, you can be my wife without benefits (wwb).
A guy can also use this term about a good female friend who he shares his life with but isn't attracted to physically - i.e. there's no chemistry.
Guy: I tell you everything.
Girl: I know, we should get married.
Guy: It's almost like we are. You're basically my wife without benefits.
Guy 1: How are things going the wife?
Guy 2: They're alright.
Guy 1: Just alright, eh? You guys appeared to be getting along well at the party last night.
Guy 2: Ya, we get along. Things are ok. But I'm not sure how much longer I can last in this situation. I didn't sign for a wife without benefits.
Also used where a wife won't indulge in a guy's minor fetish, like oral or spanking.
Girl on net: You married?
Guy: Well I have a wife without benefits.
Girl: You don't have sex?
Guy: Only missionary.
Girl: And that's not enough for you?
Girl: Well, why don't you get divorced and look for someone new?
Guy: It's complicated.
Girl: Well, I'm glad you admitted it, but I'm not really into married guys. Too bad, because I do enjoy benefits...