The phrase "most jelly-belly" would typically refer to someone who has a large, round belly or who looks overweight. Its antonyms, therefore, would be words that describe someone who is fit, slim, or slender. These could include adjectives such as "toned", "athletic", "svelte", "lean", "fit", and "slim". Other antonyms might include "muscular", "chiseled", "well-defined", or "toned". It's important to understand that different words may carry different connotations or meanings, so choosing the right antonym would depend on the specific context and desired effect. Regardless, the antonyms of "most jelly-belly" would generally be words that describe someone who is physically fit and healthy.