To feel or express great self-satisfaction, often in a malicious manner, is to?

The term that best captures the feeling or expression of great self-satisfaction, especially in a way that can be perceived as malicious or at the expense of others, is "gloat." This word derives from the idea of taking pleasure in one's own achievements while reveling in the misfortunes of others. When someone gloats, they often display their success or happiness in a way that is smug and can irritate those around them, enhancing the malicious undertone associated with the act.

The other choices do not convey this specific sentiment. For instance, while "gorge" and "glut" both relate to overindulgence (typically in food), they do not imply a sense of self-satisfaction or malicious intent. "Gnag," while it could suggest a form of annoyance or provocation, does not capture the essence of self-satisfaction tied to one's successes or the enjoyment of another's misfortune. Therefore, "gloat" is the precise term that encapsulates this particular behavior and attitude.