An old geezer became very bored in retirement and decided to open a medical clinic. He put a sign up outside that read: "Dr. Geezer's clinic. Get your treatment for $500, if not cured, get back $1,000." 

Doctor "Young," who was positive that this old geezer didn't know beans about medicine, thought this would be a great opportunity to get $1,000. So he went to Dr. Geezer's clinic.

Dr. Young: "Dr. Geezer, I have lost all taste in my mouth. Can you please help me?"

Dr. Geezer: "Nurse, please bring medicine from box 22 and put 3 drops in Dr. Young's mouth."

Dr. Young: "Aaagh! - this is Gasoline!"

Dr. Geezer: "Congratulations! You've got your taste back. That will be $500."

Dr. Young gets annoyed and goes back after a couple of days figuring to recover his money.

Dr. Young: "I have lost my memory, I cannot remember anything."

Dr. Geezer: "Nurse, please bring medicine from box 22 and put 3 drops in the patient's mouth."

Dr. Young: "Oh, no you don't - that is Gasoline!"

Dr. Geezer: "Congratulations! You've got your memory back.  That will be $500."

Dr. Young (after having lost $1000) leaves angrily and returns after several more days.

Dr. Young: "My eyesight has become weak: I can hardly see anything!

Dr. Geezer: "Well, I don't have any medicine for that so, here's your $1000 back" and hands him a $10 bill.

Dr. Young: "But this is only $10!" 

Dr. Geezer: "Congratulations! You got your vision back; that will be $500."

Moral of story - Just because you're "Young" doesn't mean that you can outsmart an "old Geezer"*

Remember: Don't make old people angry. We don't like being old in the first place, so it doesn't take much to annoy us.