April fooling
"I have this amazing idea!" he said. "It's everything I believe in. Imagine a world where we could..."
On and on he went, describing his vision, his hopes, and his dreams, almost out of breath by the time he finished.
She listened quietly. After a brief pause, she suddenly laughed. "Hahaha! Good one! It's an April Fool's joke, isn't it? You got me!"
"Oh, uh, yeah..." he replied. "April Fool's."