Humor can be a key to a speech's success. Hamilton Nolan explores knowing when and how to use it

It was Fashion Week, and an American Heart Association representative had to give a speech during an event at the New York Public Library. Outside the building, a huge red dress had been erected, a testament to the fashion gods. Speechwriter Joe Trapiano saw not just an oversized garment, but also an opportunity for the speaker.

"I think red dresses are going to ...