The agent asked the grandpa why he hadn't paid his taxes. The grandpa explained he earned the money through bets with other people and he was within the law. The agent was skeptical he had gained so much money through simple bets so the grandpa offered to make a bet.
He bet the agent $1000 that he could bite his own eye. The agent accepted, so the grandpa removed his glass eye and bit it. Still the agent was skeptical, so the grandpa bet him he could bite his other eye for $2000. The agent noted that the old man entered without aid and appeared to be able to see, so he accepted. The grandpa removed his false teeth and carefully made them bite his good eye.
Still the agent was skeptical. So the grandpa offered one final bet. He wagered, double or nothing, that he could stand at the corner of his desk and urinate into his waste basket across the room without a drop landing on his desk or floor. The agent thought carefully and concluded that the feat was impossible and he would win back his lost $3000 plus $3000 more, so he accepted.
The grandpa walked to the desk, unzipped and began urinating all over it, not a drop even coming close to the waste basket. The agent exclaimed at his victory as the grandson droped his head and moaned in frustration.
The agent asked him what was wrong. The young man explained that his crafty grandpa had wagered him $20000 that he could take a leak on his desk and make him happy about it before they had arrived.