"I refuse to answer that question on the grounds that I don't know the answer."

For instance, on the planet Earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much - the wheel, New York, wars and so on - whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man - for precisely the same reasons.

"I'd far rather be happy than right any day." Slartibartfast

Marvin: "I am at a rough estimate thirty billion times more intelligent than you. Let me give you an example. Think of a number, any number."
Zem: "Er, five."
Marvin: "Wrong. You see?"

DON'T PANIC.

"If there's anything more important than my ego around, I want it caught and shot now."

The ships hung in the sky in much the same way that bricks don't.

"You know," said Arthur, "it's at times like this, when I'm trapped in a Vogon airlock with a man from Betelgeuse, and about to die of asphyxiation in deep space that I really wish I'd listened to what my mother told me when I was young."
[Ford Prefect:] "Why, what did she tell you?"
[Arthur:] "I don't know, I didn't listen."

"Time is an illusion. Lunchtime doubly so."

Arthur: "Marvin, any ideas?"
Marvin: "I have a million ideas. They all point to certain death."