Petulant

Etymology

From Latin petulans, "forward, insolent, impudent," related to petere, "to seek, to attack." In its earliest English use it meant insolent or wanton, but by the eighteenth century it had shifted toward the modern sense of fretful, ill-tempered peevishness. The idea narrowed from bold impudence to the smaller, sulkier irritability we mean now.

adjective · /PET-yuh-lunt/
Childishly sulky or irritable over small things.
What it names
The peevish, pouting bad temper of someone who reacts to minor frustrations like a spoiled child.
Example
He gave a petulant shrug and refused to explain what had upset him.
Related idea
Peevish is a broad, habitual irritability; petulant adds the note of childish, sulky petulance over trivial slights.