When someone changes their personality or behavior to adapt and fit in with different people or social situations, it is often referred to as "social chameleon" or "social chameleon effect." The term "chameleon" is used because, similar to the reptile that changes its color to blend into its surroundings, these individuals alter their demeanor to blend into different social contexts.
This behavior is not uncommon and can be seen as a coping mechanism or a way to navigate social interactions more smoothly. However, it's essential to strike a balance between adapting to different situations and remaining authentic to oneself. Continually changing one's personality to please others can lead to a loss of self-identity and can be emotionally exhausting in the long run.