知底

dà jiā zhī gēn zhī dǐ yīn wèi wǒ men jīng cháng jiàn miàn cháng cháng bǎ jiǔ yán huān

大家知根知底，因为我们经常见面，常常把酒言欢。

They know who they are because now and then I see them, usually over drinks.