CASABLANCA

LISTER: 

He did it wrong, man.

CAT: 

(Having fun at their expense) 

Oh, it gets better!

KRYTEN: 

I just can't do it.

LISTER: 

You CAN; you just did it!

KRYTEN: 

I just can't do it, not when there's someone else there.  

What's a suitable human analogy?  It -- it's like trying to urinate in public lavatory when you're standing next to a man two foot taller than you.  

It's just not possible!

CAT: 

Look, what are you trying to do, exactly?

KRYTEN: 

He's trying to teach me how to lie, sir.

CAT: 

Any particular reason?

LISTER: 

Yeah!  Lyin's a vital part of your psychological defence system; you're naked without it.  

If you can't lie, then you can't conceal your True Intentions from Other People - at times, that's essential.  

I mean, like, take Nelson.  

(He holds the banana to his eye like a telescope.)

When he put the telescope to his blind eye and said, "I see no ships!"

Or like Humphrey Bogart, at the end of Casablanca, when he lies to Victor Lazslo to protect the guy's feelings.

KRYTEN: 

I understand the theory, sir.  

How many times have you made me watch that movie?  

I understand that it can be noble to lie; I just can't do it.

LISTER: 

But Kryten, you CAN do it.  

(Waving the banana) 

Look, what's THIS?

KRYTEN: 

It's a banana.

CAT leaves in disgust.

KRYTEN: 

It always HAS been a banana, it always WILL be a banana.  

It's a yellow fruit that you unzip and eat the white bits; it's a banana!