"I'm Thirsty" joke

Five minutes after being sent to bed by his father, a little boy yelled out, "Da-ddy."
"What?" the father asked.
"I'm thirsty. Can you bring me a drink of water?" asked the little boy.
"No. You had your chance," the father replied. "Now go to sleep."
Five minutes later, the little boy called out again, "Da-aaaaddy."
"What is it?" said the father.
"I'm THIRSTY," replied the boy. "Can I have a drink of water?"
"I've all ready told you NO!" the father replied. "If you ask again, I'll have to spank you!"
Another five minutes passed and the boy called out again, "Da-aaaaaaddy."
"WHAT?!?" snapped the father.
"When you come up to spank me, can you bring me a glass of water?"