A terms used by myself and almost everyone at Glen Eden Intermediate in 1980-1981. Used primarily as a form of mockery at someones embarrassment when told off by a teacher, falling over, getting tripped over e.t.c. Basically any act which invited ridicule from friends and people in the general vicinity. It was not "transmissible" nor could you give it to someone by touching them on the forehead or anywhere else.
Someone would "get the manus" through an embarrassing act - at which point everyone else would laugh and point and say "Manus" or perhaps "Manus on your undies".
This word replaced the previous and overused cries of "Shame" or "Shame on your undies" but is of uncertain origin - someone started it and it spread like wildfire. :-)
Calling the teacher "Mum" inadvertantly was a definite manus.