Season 7, Episode 10: "The Gum"

...and I believe I paid you with a 20-dollar bill...

...but you only gave me change for a 10.

-I don't think so. -Oh, I think so.

And I can prove it.

You see, I was doodling on the bill...

...and so if you have a 20 in there with big lips on it...

...well, that's mine.

Would you mind opening up the register?