"If you have a product that does something amazing, don't be afraid to demonstrate it."
One of my old creative directors used to say that to me all the time.
Problem was we never got to work on products that did anything even remotely amazing.
This Max Factor billboard by Leo Burnett is a great example of how to do a product demo.
Every time it rains the mascara runs. That's it.
So simple, yet so clever.