Well, I don't like pee in my corn flakes, but if you're concerned, why do you vape at all? Yes, using propylene glycol in inhalers DOES prove something, other wise, the FDA would not allow it.
I hate to be the one to pee in the cornflakes but - just because something is safe to eat or wear on your skin doesn't mean it's safe to vaporize and inhale. Even the fact that it is used in asthma inhalers doesn't really prove anything - because you don't hit the asthma inhaler all day and night. I'm not saying that PG is dangerous - I don't think it is - but the fact that you can eat it doesn't really prove anything.