petulant

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Unreasonably irritable or ill-tempered; peevish.
• adjective Contemptuous in speech or behavior.

from The Century Dictionary.

• Manifesting peevish impatience, irritation, or caprice; peevishly pert or saucy; peevish; capricious: said of persons or things: as, a petulant youth; a petulant answer.
• Synonyms Petulant, Peevish, Fretful, Pettish, Cross, irritable, irascible, ill-humored, snappish, crusty, choleric. The first five words apply to an ill-governed temper or its manifestation. Petulant expresses a quick impatience, often of a temporary or capricious sort, with bursts of feeling. Peevish expresses that which is more permanent in character, more frequent in manifestation, more sour, and more an evidence of weakness. Fretful applies to one who is soon vexed, of a discontented disposition, or ready to complain, as a sick child. Pettish implies that the impatience, vexation, or testiness is over matters so small that the mood is peculiarly undignified or unworthy. Cross applies especially to the temper, but often to permanent character: as, a cross dog; it often includes anger or sulkiness. Crossness as a mood may be more quiet than the others. See captious.

from the GNU version of the Collaborative International Dictionary of English.

• adjective obsolete Forward; pert; insolent; wanton.
• adjective Capriciously fretful; characterized by ill-natured freakishness; irritable.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective childishly irritable
• adjective obsolete forward; pert; insolent; wanton.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective easily irritated or annoyed