待我长发齐腰扮鬼吓死你
[dài wŏ zhăng fā qí yāo bàn guĭ hè sĭ nĭ]
Translating to something like 'Wait until my hair reaches my waist to dress up as a ghost to scare you to death'. The netizen who takes this might be trying to inject some humorous and somewhat frightening elements into his image or persona. It could be just playful talk indicating that he'll grow long enough hair to play a spooky joke on others later on.