待我长发及腰装鬼吓死你
[dài wŏ zhăng fā jí yāo zhuāng guĭ hè sĭ nĭ]
'When my hair reaches my waist, I’ll dress up as a ghost to scare you'. Uses a lighthearted, slightly mischievous tone implying future pranks or surprises when the time comes for action, typically used jokingly.