A man was riding in a cab, and tapped on the driver's shoulder to ask him something.
The driver screamed at the top of his lungs, lost control of the wheel and swerved just before slamming into a bus.
For a moment, the cab was silent, until the driver finally said, "Please don't ever do that again. You scared the daylights out of me!"
"I'm so sorry," said the passenger. "I had no idea a tap on the shoulder could scare someone so much."