Butthead

wiktionary

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From butt(“buttocks, backside”) +‎ head.

etymonline

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butthead (n.)

also butt-head, late 1980s, student slang, "objectionable person," from butt (n.6) + head (n.); perhaps influenced by butterhead, 1960s African-American vernacular for one who is a disgrace to the community. Earlier, butthead meant simply the butt end or bottom of anything (1630s).