If someone is described as being the "most thickskulled," it implies that they are stubborn, obstinate, and unwilling to change their opinions or beliefs. Synonyms for this term may include "pigheaded," "hardheaded," "bullheaded," or "mulish." These words all convey a sense of someone who is difficult to reason with, and who refuses to consider alternative viewpoints. Other possible synonyms for "most thickskulled" could include "immovable," "inflexible," or simply "unyielding." Regardless of the specific term used, the implication is always the same: this person is unshakably committed to their own ideas, even in the face of overwhelming evidence to the contrary.