short de bain
He's putting on his swimming trunks.
Il enfile son maillot de bain.
He's wearing swimming trunks.
Il porte un maillot de bain.
I don't have my swimming trunks.
Je n’ai pas mon maillot de bain.
— The Way He Looks (2014)
Don't forget your swimming trunks.
N’oublie pas ton maillot de bain.