“The shoddy sandwich knife couldn’t cut the mustard,” e.g.

PUN

Think of a playful twist on words where "sandwich knife" isn’t literal—this phrase relies on sounding like something else entirely. The answer is a linguistic trick often used in jokes or headlines.

This clue plays on the phrase "cut the mustard," which means to meet expectations or perform adequately. The sandwich knife is called "shoddy" because it fails at its job—just like a bad pun falls flat, hence the answer "PUN." The whole setup is a pun itself, using the literal idea of cutting mustard to hint at the wordplay.