"Grinning bear it" means to force a smile or pretend to be happy even when one is not. The antonyms of this phrase could be genuine happiness, authentic expression, or true emotion. Instead of bottling up emotions, it is important to allow oneself to express how they truly feel. Being authentic with oneself and others can lead to better relationships and personal growth. It is also important to recognize when one is not truly happy and take steps to improve their situation, rather than simply forcing a smile to please others. Overall, being genuine and true to oneself is much more fulfilling than grinning and bearing it.