有恃无恐恃宠而骄
[yŏu shì wú kŏng shì chŏng ér jiāo]
'You Shi Wu Kong Shi Chong Er Jiao' can be understood as 'Act with impunity and pride'. It shows a somewhat arrogant attitude with a hint of confidence. The bearer of such a username probably wants to convey that they do things without fear due to their reliance or trust from someone else who indulges them.