A penguin walks into a shop and asks the assistant: ‘Do you have any grapes?’ ‘No,’ he replies.

The same thing happens the next day, and the day after.  On the third day the assistant replies: ‘No, and if you come in asking for grapes again I will nail your flippers to the floor!’

The next day the penguin walks in and asks: ‘Got any nails?  ‘No,’ replies the assistant.   ‘Got any grapes?’ the penguin asks.   BOOM!!!