Bright-eyed bushy-tailed is an idiom commonly used to describe someone who is energetic, enthusiastic, and alert. However, there are many antonyms that can be used to describe the opposite of this phrase. Some words that can be used as antonyms for bright-eyed bushy-tailed include lethargic, sluggish, tired, apathetic, and uninterested. These words convey the opposite of vigor and vitality and suggest a lack of enthusiasm or energy. Other antonyms to consider may include exhausted, drained, fatigued, or simply, unenergetic. Whether you're describing a person, an animal, or an occasion, there are endless antonyms available to describe a lack of the bright-eyed bushy-tailed energy.