People already keep their smartphones on table in busy bars, and maybe their wallet in a back pocket. This isn't any easier to steal than that, and has way less impact than having to freeze your credit cards for instance.
Much will depend on the price of the final Glass, but if it is down to around the price of designer sunglasses, I don't see a big threat.
I dunno.. if I were using a urinal and someone grabbed the flipped-up glasses on my head, I would be in no position to either chase them or even get a description of their face.
If someone else in the area outside the bathroom has google glasses on, you could ask around and maybe get a face shot of the person running out of there.
I'm sort of fascinated (and slightly scared) by a world where google glasses are everywhere and the ability to get away with a crime in a public place is nearly impossible.