Three professors go to the nudist beach
They start reading their newspapers, when suddenly Miss Ridgewell approaches them from the Chemistry Department. The alarmed professors react immediately. Two of them hide their manhood with their newspapers, the third, however, hides his face. They politely salute the lady, who simply passes by to join her friends.
When she's far gone, one of them asks the third professor, "Why did you hide your face?"
To which the third professor replies, "I don't kno…