I had no idea spaz was an insult in 1971?! 80/81 was my reception year at school, so I put it down solely to Joey Deacon’s fame.
Although Wikipedia does seem to indicate its use as an insult increased significantly in the early 80s thanks to Blue Peter...
Surely that was a 'chinny reckon' which is usually reserved as a response for when someone was telling a tall story, usually said in a Jimmy Hill voice.
The whole tongue in front of bottom teeth and slapping back of hand was another Joey related insult that lives on to this day. My colleague...
I had to describe the derivation of Joey as an insult to 30-something work colleage the other day, and also how the word Spastic only became a pejorative term in British English thanks to Blue Peter in 1981.