The idiom "kept one's shirt on" is typically used to describe a situation where someone has remained calm and composed in the face of a difficult or frustrating situation. Some possible synonyms for this expression could include "stayed cool", "remained level-headed", or "maintained composure". Other related phrases might include "kept a clear head", "held one's tongue", or "refrained from losing one's cool". Generally, these expressions all convey a sense of restraint and self-control in the face of challenging circumstances, highlighting the importance of remaining calm and collected in order to navigate difficult situations successfully.