柠檬不甜
[níng méng bù tián]
This username '柠檬不甜' translates to 'Lemon is not sweet.' It plays on the usual sourness of lemon. The user likely means that their personality or life experience defies expectations - in this case, they might have experiences or character traits which are contrary to what people may expect. They might be sweet where sourness (negative emotions) would be anticipated.