at one's expense
01
彼の費用で, 彼のお金で
used to say who has paid for something
idiom
例
The document was printed at the taxpayer's expense.
その旅行は会社の費用で手配された。
02
(particularly of a joke) in a way that causes harm to someone or makes them embarrassed
disapproving
idiom
例
He told a joke at her expense, which left her feeling humiliated in front of the entire group.
