Term used at Linwood High School, Christchurch, NZ in the 80's for kids who pretended to be punks in the weekend. Of course everyone who is a punk is pretending.
The precise history of the term is unclear, but it may be related to "Sunday Driver" a term formerly used for people who only take their cars out of the garage, on Sundays, for slow, scenic drives in the country. After a wash and wax it is parked back in the garage for another seven days.
Hey dude, did you see the Sunday Punks in the square this weekend?
Yeah, they looked like a couple of Nana's with their clip-on earrings.