Sheldon Cooper: I found the perfect wedding date.

Amy Farrah Fowler: That's terrific!

Sheldon Cooper: No, it's not. It was May 19, 1996. We would have had a lovely wedding.

And our honeymoon would have coincided with the first appearance of the Hale-Bopp comet.

Amy Farrah Fowler: Sheldon, you were 16.

Sheldon Cooper: And in Texas... no one would have batted an eye. Oh, wait, it's no good. That's the day that Jon Pertwee, the third Doctor Who, died.

Amy Farrah Fowler: And it's in the past!