There are several antonyms for the term "classic exemplar," which refers to a perfect or model example of something. One such antonym might be "ordinary," which implies that something is average, mediocre, or lacking in exceptional qualities. Another antonym could be "defective," suggesting that something is flawed, imperfect or sub-standard in some way. "Atypical" could also serve as an antonym, implying that something is unusual, rare or divergent from the norm. Finally, "non-standard" could be used as an antonym for "classic exemplar," indicating that something does not meet established or accepted criteria for excellence.