Jennifer Siebel and Bevan Dufty share a guffaw during today's "501 Day," a benefit supporting Goodwill. If you bring in a pair of old denim to the Castro or Union Square Levi's stores, you will receive a 25% discount on a new pair. Read more about "501 Day," if you want to help out, right here.

(Note: Be careful NOT to donate San Francisco-made Levi's. You'll want to keep those. If you plan on giving away an old pair of Levi's, first check the buttons to see where it was made.)