In 1985, one Sean J. Connolly coined the phrase "jump the shark", which his friend John Hein would use as the name of his web site 12 years later. For those of you who haven't been keeping up with your pop culture, here's the definintion of "jump the shark", taken from the site:

Q. What is jumping the shark?

A. It's a moment. A defining moment when you know that your favorite television program has reached its peak. That instant that you know from now on...it's all downhill. Some call it the climax. We call it "Jumping the Shark."  From that moment on, the program will simply never be the same.

"Jumping the shark" comes from the fifth-season episode of Happy Days in which the Fonz accepts a challenge from a rival to waterski-jump over a shark. The rival chickens out at the last minutes, but the Fonz is too cool to win by forfeit and makes the jump anyway. I have vague memories of this episode (remember, this was September 1977 and I was 9) but I understand how "jumping the shark" became synonymous from "it's all downhill from here."

If you've never seen the "jumping the shark" moment, you're in luck: someone recently posted it in Windows Media format [2.5 MB, enclosure], and it's even cheesier than I remember. Especially since the Fonz does the jump wearing his stolen-from-Brando trademark leather jacket/white T-shirt combo.