in one’s birthday suit

(adjective) completely naked

Example Sentences:

The patient was forced to be in his birthday suit for his medical exam.

All of the people in the nudist colony enjoyed being in their birthday suits.

Media:

Similar idioms:

1. stark naked
2. in the flesh
3. in the nude
4. in the raw
5. buck-naked
6. in the buff
7. butt-naked