"Doeth best" is an idiomatic expression which means to put forth one's best effort or to do one's utmost. Antonyms for this phrase would include words or phrases that convey the opposite meaning such as "half-hearted", "slack", "negligent", or "indifferent". These antonyms suggest a lack of effort or a careless attitude towards a task or responsibility. Other antonyms could include words like "worst", "unproductive", "incompetent", or "inefficient", which indicate a complete lack of success or the inability to achieve a desired outcome. It's important to keep in mind that antonyms for "doeth best" vary in degree, ranging from mild indifference to complete failure.