I have to pick just one? That's a tall order, I can't limit myself, so I'll list a few:
My Mother the Car
I Love Lucy in all its variations
Star Trek--the original series
Okay, I have to admit Star Trek isn't the worst, but looking back on it now, it's really bad--bad acting, bad production values, bad writing. It's a wonder it ever found its audience and led to the good shows (STTNG, DS9) that followed.