I was at RAF Tern Hill in 1968, which in those days was the location of Central Flying School (Helicopters).
On our basic instructors course was a variety of guys from all services, though one in particular stood out from the rest of us. He was a Wing Commander RAF CFI A1, who had converted to helicopters, and needed to complete a helicopter instructors course.
One of our mentors was an RAF Sqn Ldr 'Schoolie' who took us for 'Instructional Technique' lessons. Our first task was to produce a 5 minute lecture on a subject of our choice so that the Schoolie could highlight our bad points. The Wg Cdr, very politely, asked if the Schoolie really wanted him to present a 5 minute lecture, as he was already a fixed wing A1 Instructor with 7000hrs, and didn't want to waste anyones time.
The frosty reply was that we were all course members, and the Wg Cdr was to give a 5 minute lecture!
On the given day, the Wg Cdr gave a brilliant lecture entitled, 'How To Suck Eggs Better Than Your Grandmother'.
He produced straws and eggs for each member of the course, and then gave us detailed instructions on how to place the egg, and hole it, in order to suck out the contents.
The Schoolie never picked up on the sarcasm, and admitted it was an unusual choice of subject, but extremely well presented.