The incident with the introductory flying lesson with the guy freezing on the controls, will always give you grey hairs. Many a time you would have to smile through gritted teeth at the family member on the weekend with the rest of the ice cream lickers, and still ask if he would still like to do a licence.
Luckily for me it never happened, but very close on occasion. Even with experienced instructors sometimes it is just plain luck that you managed to recover the aircraft with someone trying to kill you.
Fluffy