"Full of beans" is commonly used to describe someone who is energetic, lively, and enthusiastic. However, if you're looking for antonyms for this popular phrase, you might consider terms like lethargic, apathetic, or dull. Someone who is feeling lethargic may lack energy, motivation, or interest in their surroundings. Likewise, an apathetic individual may be disinterested, uninspired, or lacking in passion. And, when someone is feeling dull, they may be unexciting, unstimulating, or unengaging. Thus, when searching for an antonym for "full of beans," consider terms that evoke a sense of sluggishness, disinterest, or boredom.