not know what hit you
US /nɑt noʊ wʌt hɪt ju/
UK /nɑt noʊ wʌt hɪt ju/

1.
tidak tahu apa yang menimpa, terkejut sepenuhnya
to be completely surprised or overwhelmed by something, often something negative or sudden
:
•
When the market crashed, many investors didn't know what hit them.
Apabila pasaran jatuh, ramai pelabur tidak tahu apa yang menimpa mereka.
•
The boxer landed a punch so fast, his opponent didn't know what hit him.
Peninju itu melancarkan tumbukan begitu pantas, lawannya tidak tahu apa yang menimpanya.