得瑟的疯纸
[dé sè de fēng zhĭ]
This username 'A Crazy Sheet Being Cocky' implies the user is a carefree and boastful person. '得瑟' suggests that they like showing off or being silly sometimes. '疯纸' literally means crazy paper which metaphorically suggests a free soul not confined by many rules, like how paper can fly freely in the wind.