Bill and Doug went into a diner that looked as though it had seen better days. As they slid in 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 into the kitchen. Two minutes later, she was back. 

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