My Mother in Law wants to borrow my wife's thumb ring so her boy friend can wear it on his ring finger.

My wife's mother has a boy friend of several months after he moved in with her from Puerto Rico. He hasn't worked since he moved here and claims to be unemployable because of the language barrier. He recently lost his wedding ring (currently married to someone else), and now my mother in law wants my wife to lend them her thumb ring so they can pretend to the world their married. I find this totally bizarre, and I'm shocked, and pissed that a man would want to wear my wife's jewelry, as opposed to finding his own way of recovering his lost. Is it me????