老油条
Oily and wily
【注音】lǎo yóu tiáo
【解释】“油”给人一种滑溜的感觉，油条满身是油，比喻处事圆滑、社会经验极其丰富的人，从感觉上是恰如其分的。
You has a extended meaning of “slippery” or “foxy”. As youtiao (deep-fried twisted dough sticks, the most common Chinese breakfast) is oily from end to end, it’s not hard to understand why this expression came to mean those worldlywise people who are experienced and wily.
【例子】
例：那位赵老板可是个老油条，跟他打交道可要分外小心。
Ex.：That Manager Mr. Zhao is a wily old bird, you’ve got to be extremely careful when you have dealing with him.
露马脚
Give oneself away
【注音】lòu mǎ jiǎo
【解释】这就跟说“露出了狐狸尾巴”一样，表示露出了破绽。
Another similar expression is “showing the fox’s tail”, meaning let the cat out of bag, or give the game away.
【例子】
例：这位自称是香港商人的人终于露出了马脚，原来他是一个骗子。

Ex.：The self-claimed Hongkong merchant finally revealed his true feature of a quack.