The phrase "knocking dead" is often used to describe something that is highly successful or impressive. However, there are several antonyms that can be used to convey the opposite meaning. Some of these could include underwhelming, disappointing, lackluster, unremarkable, or mediocre. Additionally, words like unimpressive, uninspiring, unspectacular, or unsuccessful could also be used as antonyms for "knocking dead." Depending on the context and the intensity of the original phrase, one antonym may be more appropriate than another. Regardless, by using these antonyms, we can express the idea of something falling short of expectations or not achieving the desired outcome.