很2先森不3菇凉
[hĕn 2 xiān sēn bù 3 gū liáng]
This nickname expresses someone who may have a playful or mischievous personality. '先森' and '菇凉' are internet slang for 'mister' (or guy) and 'girl'. So the person may feel that they're somewhat a boy but also not completely a girl, which might refer to someone who's young, not fully grown up, in their adolescence.