The phrase "acts cool" can be understood as showing off an attitude of confidence, composure or detachment. Antonyms for this phrase could include descriptions of someone who is nervous, anxious, flustered or unsure. Instead of showing off a confident demeanor, someone who is antonymously "acting cool" might be fidgeting, stuttering, sweating or apologizing frequently. Other antonyms could include words that suggest a lack of poise, such as awkward, bumbling, or clumsy. Overall, antonyms for "acts cool" describe behaviors or traits that are the opposite of confident, collected, or nonchalant.