One who douches, or a device that delivers douches; also a person who ducks or dives.
From douche plus the agent suffix '-er,' meaning one who performs the action of douching or ducking. This is a straightforward English formation.
The term 'doucker' shows how English speakers readily create occupational or descriptive nouns—if you douche, you're a doucker, but the word also carried medieval connotations of someone who was nimble or evasive.
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