人不得瑟枉少年
[rén bù dé sè wăng shăo nián]
This phrase roughly means that one should live freely during youthful years because life is too short for caution and reserve all the time. 'Not being happy enough to make yourself look foolish when you are young would be a regret'. This internet name implies that the user enjoys living in an unrestrained fashion and celebrates his/her youth.