zipperhead · noun1
From zipper + head, in reference to the leather helmets used by early Canadian armoured crewmen, which had zipper-like stitching.
zipperhead · noun2
Coined by US soldiers during the Vietnam War, apparently from zipper + head. The semantic motivation is unclear. One theory is that the Vietnamese were so called because their heads would split open in zipper-like fashion if they were shot in the right way; another is that zipper-like tracks would be left on them if they were run over by jeeps or tanks.
Etymology from Wiktionary, CC BY-SA 4.0.