You may find that humorous but it's not humor. It's playing the role you said it should. According to the script, "I'm sorry, Dave. I'm afraid I can't do that."

You may find that humorous but it's not humor. It's playing the role you said it should. According to the script, "I'm sorry, Dave. I'm afraid I can't do that." is said by HAL more than any other line HAL says.