你明天不把钱还给我，我就不客气了。
I pity you (ie I am threatening you) if you can't pay me the money by tomorrow.
如果你需要什么东西，请不客气地对我说。
In case you need something, please don't hesitate to let me know.
那位顾客对女店员不客气的回答感到忿怒。
The customer was angry with the salesgirl for her impolite answer.
