John is caught doodling in class.
"Mr. Lennon?" his teacher called. "Mr. Lennon, what do you think you're doing?"
John looked at him. "Listening to you ramble on about antibodies, sir," was his laconic answer, making some of his fellow pupils chuckle.
His teacher frowned. "No, Mr. Lennon, we've moved on to exponents. I'd appreciate it if you'd pay attention to my lectures for a change."
"But that's the thing," John protested. "What am I ever gonna even do with this kind of crap? If I'm going to play guitar, how could I even use it?"
"Playing guitar for a living will pulverize your brain," his teacher said sternly.
"Then let it pulverize away," John replied as he hopped out of his chair. "I'm out of here." Before his teacher could argue once more, John dashed out of the room, humming in perfect tempo.