be big of someone idiom informal disapproving
（某人）真好心，好慷慨（通常用作反语，表示幽默或气愤）
If an action is big of someone, it is kind, good, or helpful. This phrase is usually used humorously or angrily to mean the opposite.
You can spare me an hour next week? That's really big of you! 下周你能为我抽出1个小时？你可真慷慨！