Petulant is an adjective used to describe something or someone as being rude or disrespectful, especially when said person is disappointed or denied a desire. It is commonly associated with children who throw tantrums and adults who may act like children who throw tantrums.
The adverb form is petulantly and the noun form is petulance.
Impetuous is an adjective used to describe something or someone as being or doing things that are not thought out or researched, someone who makes rash or unplanned decisions. It can also describe something as traveling fast or with force, but this definition is much less common.
The noun form can be either impetuosity or impetuousness, and the adverb form is impetuously.
Examples
Sure, Bowman faces some routine challenges: the ugly 2015 budget, hiring a new CAO, and high odds that Premier Greg Selinger’s government will be petty and petulant in response to an unfavourable outcome. [CBC]
George Osborne, chancellor of the exchequer, has petulantly threatened to cut off access to Scotland’s favourite beverage — not its world-renowned Scotch, as one might be forgiven for thinking, but a potent concoction called Buckfast Tonic Wine, which is high on alcohol, caffeine and other tantalising chemicals, and low on price. [The Indian Express]
He’s had a tremendous amount of success, and it would be foolhardy of me to make an impetuous decision. [NBC Sports]
Clamens has taken refuge in Amsterdam, preferring the canals’ still water to the Seine’s impetuous flow, and he likes to confide in strangers. [Camus]
In my opinion, we must
guard ourselves from being swept away by the impetuous tide of fashionable wisdom, as time and time again, it proves to be an exaggeration and a faulty base for damaging long-run legislation. [The Yorkshire Post]