at (someone's) expense

Translations
за счет (кого-то)
The company held a party at the CEO's expense.
Компания устроила вечеринку за счет генерального директора.
Definitions
At someone's expense means that something is done in a way that causes someone to suffer a loss, disadvantage, or cost, often for the benefit or amusement of another person.
Words
expense

noun
расход