He's so hung-up about his appearance that it affects his self-confidence.

hung-up 是由动词短语 hang up（挂断电话、悬挂）演变而来的形容词，这里表示"过分在意"或"纠结于"某事的状态。hung-up 常用来形容对某件事过度关注或焦虑的心理状态。