The antonym for "keeping shirt on" is "taking shirt off." This phrase can imply different meanings and contexts based on the situation. In some cases, taking one's shirt off indicates confidence, strength, or dominance, while in other cases, it could indicate vulnerability, weakness, or surrender. Moreover, taking a shirt off is often associated with physical activities like swimming, exercise, or outdoor work. In some instances, it could be considered socially inappropriate to take off one's shirt, especially in public or formal settings. However, the antonym "taking shirt off" is more versatile and can be interpreted based on the speaker's tone, body language, and cultural significance.