我非美人但心如毒蝎
[wŏ fēi mĕi rén dàn xīn rú dú xiē]
'I'm Not A Beauty But My Heart Is As Venomous As A Scorpion' describes someone admitting they don't have beauty, but their heart harbors strong will or ruthless thoughts, perhaps even maliciousness. Sometimes it carries the implication of self-consolation or sarcasm.