This set of stickers, which was also a card set as well, was part of the larger 'wacky stickers' trend which Fleer enjoyed during that time period. They basically consisted of insulting decals that a kid could surreptitiously slap onto a schoolmate's locker, such as 'I'm the Class Brat' or use in more specific situations such as 'This Butcher Sells Pure Horsemeat.'
When the stickers were peeled off, kids could collect the remaining cards as they, too, carried an illustration. In fact, the cards carried the same 66 illustrations that were on the stickers, although it was apparently arranged so that the same image did not repeat between a sticker and its backing; every sticker apparently featured one of two reverse images. The cards are designated 'Insult Cards' while the stickers say 'Insult Stickers'.
These were sold in packs of 6, including 1 stick of gum, with 2 pack variations known.