城府再深不及你狠人心再狐不如你毒
[chéng fŭ zài shēn bù jí nĭ hĕn rén xīn zài hú bù rú nĭ dú]
This implies the person considers themselves very experienced or cunning but admits another person is more devious or 'poisonous' (toxic). It's a form of admiration towards someone crafty and shrewd.