Comparative form of bratty; more spoiled, disobedient, or obnoxiously childish than something or someone else.
From brat plus -y (creating an adjective) plus -er (comparative suffix). The progression brat → bratty → brattier follows standard English comparative adjective formation.
Psychologists notice that 'brattier' is almost always used for children—we rarely call adults brattier even if they're more obnoxiously demanding, which shows how language encodes our expectations about aging.
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