That Must be Painful_英语成人笑话

while out one morning in the park, a jogger found a brand new tennis ball, and seeing none around it might belong to, he slipped it into the pocket of his shorts.
later, on his way home, he stopped at the pedestrian crossing, waiting for the lights to change.
a girl standing next to him eyed the large bulge in his shorts.
"what's that ?" she asked, her eyes gleaming with lust.
"tennis ball," came the breathless reply.
"oh," said the girl sympathetically, "that must be painful.... i had tennis elbow once."