When it comes to describing someone as touchy or irritable, the word "tetchiest" perfectly encapsulates its essence. However, there are several equivalent synonyms that can convey the same meaning in a slightly different manner. One alternative could be "petulant", which emphasizes an overly sensitive or peevish temperament. "Testy" is another suitable synonym, highlighting someone's short-tempered or easily aggravated nature. Additionally, one could use "cranky" to emphasize a person's grumpy or ill-tempered disposition. Lastly, "irascible" serves as a more formal synonym, denoting a tendency to become easily provoked or annoyed. Each of these synonyms captures the essence of "tetchiest" through different shades of meaning.