- at one's best
- at one's best1. and at its best to the utmost; to the highest degree possible. •
This restaurant serves gourmet food at its best.
•The singer was at her best when she performed ballads.
2. in the best of health; displaying the most civilized behavior. (Often in the negative.) •He's at his best after a good nap.
•I'm not at my best when I'm angry.
* * *{prep. phr.} In best form; displaying one's best qualities. * /Tim is at his best when he has had a long swim before a ballgame./ * /Jane rested before the important meeting because she wanted to be at her best./
Dictionary of American idioms. 2013.