心眼比牙床還松动
[xīn yăn bĭ yá chuáng huán sōng dòng]
This nickname expresses that the person is cunning or sly, using a hyperbolic expression in Chinese culture. 'Heart' and 'mind' represent one's inner thoughts, 'loose' means not restrained; it implies someone who doesn't keep promises or change positions easily.