A person who gloats; someone who takes smug satisfaction in another's failure or misfortune.
From gloat + -er (agent noun suffix). The -er suffix creates nouns for those who perform the action, appearing in teacher, baker, runner, etc.
Gloater is that person everyone knows—the one who smiles just a little too widely when a rival fails. The -er suffix makes them a type of person defined by this one quality, suggesting it's habitual rather than occasional.
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