Allen: Let's have a dinner at Red Rose Restaurant. 我们去红攻瑰餐厅撮一顿吧。

Mary: Who's on it? 谁请客?

Allen: I got a rise. Dinner is on me. 我加薪水了，我请客。

解析： 该句用于含蓄地表达自己的请客意愿，比说I'll pay for the dinner.要婉转。on在句中为介词。当然并不固定于dinner。我们也可以说It's on me．或者The wine is on me．(酒钱我来出。)都是可以的。