The term "most oversensitive" can have many antonyms, depending on the context in which it is used. If we're talking about emotional sensitivity, antonyms could include "unemotional," "detached," "unfeeling," "impervious," or "stoic."
If we're looking at oversensitivity in the context of criticism or feedback, antonyms might include "resilient," "thick-skinned," "impervious," or "insusceptible."
Overall, antonyms for "most oversensitive" tend to be words that convey a sense of emotional resilience or detachment, as opposed to sensitivity and reactivity. By cultivating an opposite attitude, we can learn to manage our reactivity and have a more balanced emotional life.