The phrase "whiz bang" typically refers to something that is impressive or highly effective, often used in the context of technology or innovation. Some possible antonyms for this term might include words like dull, mediocre, or unimpressive. Other antonyms might include words like slow, outdated, or obsolete, emphasizing a lack of speed or modernity. Alternatively, words like unremarkable, unexceptional, or commonplace might emphasize a lack of uniqueness or originality. Ultimately, the antonyms for "whiz bang" will depend on the specific context and the characteristics being emphasized.