One day while jogging, a man noticed two tennis balls lying by the side of the road. He picked the balls up, put them in his pocket and proceeded on his way. 
Waiting at the cross street for the light to change, he noticed a beautiful blonde standing next to him and smiling. 

"What are those big bulges in your running shorts?" she asked. 

"Tennis balls," answered the man, smiling back. 

"Wow," said the blonde, looking upset. "That must hurt. I once had tennis elbow and the pain was unbearable."