in your birthday suit
US /ɪn jʊər ˈbɜrθ.deɪ suːt/
UK /ɪn jʊər ˈbɜrθ.deɪ suːt/

1.
一丝不挂, 赤身裸体
naked; without any clothes on
:
•
He was caught running around the garden in his birthday suit.
他被发现在花园里一丝不挂地跑来跑去。
•
She felt embarrassed to be seen in her birthday suit.
她觉得被看到一丝不挂很尴尬。