The phrase "tried on for size" means to test or experiment with something to determine its suitability or fit. Antonyms for this phrase could include "rejected outright," meaning something is deemed unsuitable and not even given a chance to be experimented with, or "accepted blindly," meaning someone agrees to something without any prior testing or examination. Other antonyms could include "decided without consideration," "dismissed without thought," or "ignored entirely." Each of these antonyms implies a lack of thorough evaluation or consideration that is inherent in the act of trying something on for size.