catch someone with their pants down
US /kætʃ ˈsʌm.wʌn wɪð ðer pænts daʊn/
UK /kætʃ ˈsʌm.wʌn wɪð ðer pænts daʊn/

1.
застать врасплох, поймать с поличным
to discover someone doing something wrong or embarrassing, or to find them unprepared for something
:
•
The boss caught him with his pants down when he was playing games on his computer during work hours.
Начальник застал его врасплох, когда он играл в игры на компьютере в рабочее время.
•
The sudden inspection caught many employees with their pants down, as they hadn't prepared their reports.
Внезапная проверка застала многих сотрудников врасплох, так как они не подготовили свои отчеты.