Superlative form of bratty; the most spoiled, disobedient, or obnoxiously childish.
From brat → bratty → brattiest, following standard English superlative formation with the -est suffix added to the adjective.
The word 'brattiest' sounds almost playful, which is why parents use it affectionately—but linguists notice we'd never say a boss is being 'brattiest'; the word itself linguistically confines bad behavior to childhood.
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