待我长发及腰做鬼吓你
[dài wŏ zhăng fā jí yāo zuò guĭ hè nĭ]
'When My Hair Reaches My Waist, I'll Be a Ghost to Frighten You'- It’s a humorous way to refer to a promise or a lighthearted threat using traditional concepts such as growing long hair (indicative of time) and referencing folklore about ghosts.