Ravirn: If I tell you, there's absolutely no way you're going to believe me.
Eris: I don't believe you.
Ravirn: What did I just tell you?
Eris: That I wouldn't believe you. But that's got nothing to do with my not believing you.
Ravirn: I know that, because I know why you don't believe me.
Melchior: (*facepalm*) I don't believe this.
Rufus: You're not going to believe this.
— So Random!, right before saying something that's completely ridiculous, but ultimately turns out to be true.
"You would not believe what I've been through tonight."
—Mr. Potato Head, Toy Story 3