你别慌张我知道你在说谎
[nĭ bié huāng zhāng wŏ zhī dào nĭ zài shuō huăng]
Directly translates to 'Don't panic, I know you're lying'. It expresses confidence in detecting untruthfulness. The user seems not only certain about calling out lies but also showing indifference towards it, adding a nuance of cool observation and judgmental attitude.