Bill and Doug went into a diner that looked as though it had seen better
days.  As they slid in to a booth, Bill wiped some crumbs from the seat. 
Then he took a napkin and wiped some moisture from the table.  The
waitress came over and asked if they wanted some menus.

"No thanks," said Doug.  "I'll just have a cup of black coffee."

"I'll have black coffee too," Bill said.  "And please make sure the cup is
clean."

The waitress shot him a nasty look.  She turned and marched off in to the
kitchen.  Two minutes later, she was back.

"Two cups of black coffee," she announced.  "Which one of you wanted the
clean cup?"