The third Hokage was visiting Tsunade for his yearly checkup.
"We're all done here, Mr. Sarutobi," Tsunade made some important medical notes on her fancy doctor's clipboard. "But I'll need a stool sample, a urine sample, and a sperm sample."
"What? What did you say? What do you need?" Sarutobi, being the old man that he was, had a hard time hearing things.
Tsunade sighed. "I need your underwear."