The barber looks around the shop and says, "About 2 hours."

The guy leaves

A few days later the same guy sticks his head in the door and asks, "How long before I can get a haircut?"

The barber looks around the shop full of customers and says, "About 2 hours."

The guy leaves

A week later the same guy sticks his head in the shop and asks, "How long before I can get my haircut?"

The barber looks around the shop and says, "About an hour and a half."

The guy leaves

The barber looks over at a friend in the shop and says, "Hey, Bill, follow that guy and see where he goes."

In a little while, Bill comes back into the shop laughing hysterically

The barber asks, "Bill, where did he go when he left here?"