What's the proper way for a guy to communicate that he isn't interested in a second date?

The date wasn't horrible. There just wasn't any spark. Food is my life and it's not really a topic for her, she loves to sleep, I sleep about 5 hours a night etc. Anyway, usually when women I go out with don't want a second date, they simple screen calls or make up some excuse like - It's really busy at work - and I'm expected to know what that really means. Well, I did the same with this woman that I went out with and my best friend, who is a woman, said I was being a jerk. Doesn't it work both ways? And if not, why not?