Petulant (adjective)

1. Behaving in a bad-tempered or irritable way, especially over minor matters.
2. Childishly sulky or peevish.

Origin:

From the latin word petulans meaning "impertinent, forward".

Examples:

1. The child was petulant when she didn't get her way.
2. She was petulant with the waiter, complaining about the slow service.
3. He was petulant and refused to answer any more questions.
4. The customer was petulant because the store was out of stock of the product they wanted.
5. She was petulant when she didn't get the promotion she wanted.