Post jokes that are funny the first time you see it, but get less funny when you what's going to happen.
From Homer The Heretic:
"Kids, let me tell you about another so-called wicked guy. He had long hair and some wild ideas. He didn't always do what other people thought was right. And that man's name was...I forget. But the point is...I forget that, too. Marge, you know what I'm talking about. He used to drive that blue car?"