以为你是人原来你是狗
[yĭ wéi nĭ shì rén yuán lái nĭ shì gŏu]
This phrase sarcastically expresses disappointment with someone's betrayal, meaning 'I thought you were a human (someone trustworthy/respected) but you turned out to be a dog (unworthy of respect)', implying the person feels let down in a harshly accusatory tone.