Antonyms for the word "most high caliber" can include phrases such as "lowest quality," "low standard," or "poorly-made." These antonyms describe something that is inferior, lacking in skill or craftsmanship, or otherwise subpar. Other antonyms might include "mediocre," "inferior," or "unsatisfactory," which denote something that is not quite up to par or does not meet expectations. These antonyms serve as a reminder that the word "most high caliber" implies a level of excellence or quality that is not always present in everything we encounter, and that there are many things in the world that fall short of this standard.