The part I always show people is when Zabuza was performing the seals to do the water dragon, and Kakashi was mimicking his movements. The two of them were standing there facing each other performing lots of seals and chanting in cool voices. That usually works when trying to hook people.

But I agree with what a few people have said, you really have to watch the series from the beginning to get a true sense of the characters - showing scenes or entire eps from later in the series is a form of major spoiling if they're gonna watch later.