Zipperhead

From zipper + head. From the leather helmets formerly used by early Canadian armoured crewmen, with a pattern of stitching resembling a zipper. There is also a folk etymology referring to the zippers on armoured-vehicle crew suits (repurposed flight suits).

1960s–1970s, zipper + head. Used by soldiers during the Korean and Vietnam Wars; multiple hypotheses exist as to the specific origin. One is that if an East Asian person were shot in the middle of the forehead with a machine gun, the head would split as if being unzipped; another is that the appearance of tire or tank tracks on a body which had been run over by a military Jeep or tank resembled a zipper.