Doctor's note (n) An excuse for any occasion.
Any behavior or affectation wherein you might draw attention or comment might be explained away with : "It's okay, I have a doctor's note".
Jasmine : "Dang - What's up with Cedric's shoes ? Who'd wear those to the club ?!"
Bennie: "S'okay - he has a doctor's note."
Mags: "You were so rude to that clerk !"
Cooper : "I have a doctor's note."