What is the worst episode of your favorite TV show?S

This weekend is all about the DVD marathons, and chances are you'll be revisiting your favorite TV show. Except for that one episode, the one you always leapfrog over. You know the one. So tell us. What's the most horrible episode of your favorite show?

Please include a clip or picture of this travesty of an otherwise excellent show. And let us know the show and episode title, and why it blows so many chunks. Thanks!

Top image: Buffy the Vampire Slayer, "Beer Bad".