what would jesus do?

I don't understand the whole, what would jesus do phenomenon. is it supposed to temper people from making hedonistic decisions? it seems so open to interpretation. like, if I lived my life by, what-would-jesus-do, I would assume that he would live my way.

here's an example:

I'm at the checkout line at whole foods and I have a quart of hot food from the hot food bar. the checkout girl says, "is that soup?" the soup is $6. otherwise they weigh it and it costs double.

what would jesus do?

I think if he were on a budget and was low on shekels, he'd say it was soup.