Do Tell: Is It Bad Luck to Try on Someone's Ring?

It's been said that trying someone's engagement ring on your left ring finger is bad luck for single women. Why? I'm not sure, but even though I know it's just an old wives tale, it's one superstition that I don't want to test! Since I love to try on engagement rings, I always slip them on my right hand, just in case. But what about you? Ladies, do tell, when you try on your a friend's engagement ring, do you put it on your right or left hand?