spoiled brat

A spoiled brat is a child who has been overindulged to the point of becoming demanding, ungrateful, and poorly behaved.

The term extends to adults who act entitled or throw tantrums when they don't get their way: He's a spoiled brat who's never heard the word no.

Brat alone can mean the same thing, but *spoiled brat* emphasizes that upbringing—not just temperament—is to blame.