If you're a fan of Abbott and Costello, and you believe someone might ask you for your password, try this one:

"I always forget, so I wrote it down."

A: What's your password?

B: "I always forget, so I wrote it down."

A: Where?

B: Where what?

A: Where did you write down your password?

B: I don't write down my password.

A: You just told me you did!

B: Why would I do that?

A: Because I was asking you for your password.

B: And I gave it to you.

A: Did you, or did you not, forget your password?

B: No.

A: So let's have it.

B: "I always forget, so I wrote it down."

A: Do you... ah... need to search your pockets?

B: Why?

A: To help you remember.

B: Remember what?

A: Your password.

B: No. It's very distinctive. I always remember it.