Isn’t this a bit inappropriate?

 Liu Si Si might not have understood the deep underlying meaning behind his words, but she understood his sarcastic remark. "Next time, you don't get to threaten my friend." She warned in a very serious tone. 

And Lu Xifu's lips turned up, finding her bossy attitude quite adorable. "Did I threaten her? I don't remember anything such." He denied it straight on her face, making her eyes go sharp at him. 

Even though he had masked it well, Yun Meiyi read it well. It was subtle, he might not be really serious about it. But with Si Si, she couldn't risk it. So, she wanted him to know that as well. 

"I might not know you well enough. But I have come to understand that you love your narcissist attitude the most. She is human and unknown to your devilish powers and world. So, keep it that way. Don't involve her in the matters." She said and at her words like that he gave out a deep chuckle.