A person who specializes in or theorizes about antipathies, or someone who is characterized by having many antipathies.
From antipathy + -ist (one who does or believes in). This follows the pattern of dozens of -ist words in English, though antipathist is quite rare and mostly historical, appearing in 19th-century philosophical texts.
An antipathist in the 1800s was someone who catalogued and theorized about natural dislikes—thinking that everything had natural enemies and affinities. It was a serious philosophical position before it became old-fashioned.
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