be on somebody （口語中使用）某人來買單
It's on me.
我買單。
The drinks are on me！
飲料我來買單！

What's somebody on? (口語中使用）指某人行為異常，像磕了藥，吃錯了藥一樣
What are you on?
你吃錯什么藥了？你嗑藥了？

having something on (informal) （預先安排的事）將發生
I haven't got anything on tomorrow.
我明天還沒有安排。

be on for something(informal) 想要做某事
How many of you are on for a drink after work today?
有幾個人下班要去喝一杯呀？
Is anyone on for a drink after work?
有人想下班后去喝一杯嗎？

I'm on it. 我馬上做。

be/go/keep on somebody(informal) 抱怨，嘮叨，發牢騷
Stop keeping on about it!
別再嘮叨那件事了。
I wish you wouldn't go on at me the whole time.
我希望你不要一直跟我抱怨。

you're on (口語中使用）賭就賭吧。
I bet you're wrong.
我打賭是你錯了。
You're on.
賭就賭吧。