A person who bickers; someone who argues frequently about small, unimportant matters.
Derived from bicker (to argue) plus the agent suffix -er, which creates a noun describing someone who performs the action. The formation is straightforward English word-building.
Every workplace has a bickerer, and this perfectly cromulent English word hasn't made it into every dictionary because it's so specific to human social dynamics that new generations have to rediscover it.
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