The antonyms for the phrase "doest best" include "underachieve," "fail," and "underperform." When we say someone "doest best," we are implying that they are performing at their optimal level, doing everything they can to achieve success. However, the opposite of this phrase suggests that someone is not performing up to their full potential or achieving their goals. It is important to remember that not everyone can be at their best all the time, but by acknowledging and recognizing the antonyms of "doest best," we can strive to improve and reach our full potential.