Crotchety is most often used when talking about older people, like the crotchety old man who sits on his porch and yells at you to slow down when you drive by. Sometimes crotchety people take pleasure in bothering others or complaining. Crotchety derives from the word crotchet, meaning "whim or fancy," and crotchety people do seem subject to whims — you might not know exactly why they're irritable, but you definitely know they're crotchety.