You are indeed a hard nut to crack.
2 seconds sound clip from the Invincible Super Chan (1971) movie soundboard.
You can hear this line at 00:32:47.666 in the DVD version of the movie.
Quote context
[...]
- All I want is Mo Yinshan, so why don't you bring him to me?
- You haven't a chance! I'll overcome you all!
- I thought it best that I should warn you.
- Mo Yinshan is on his way. He'll arrive soon. I thought you ought to know. In case it's another trap.
- You are indeed a hard nut to crack.
- Go, Chan, win your little joust. Beat Mo Yinshan.
- Then you and I will duel. I'll win and be known as the greatest fighter in the land.
- Daughter, stay out of this. It is our concern. We will fight this man fairly.
- Ah, there's nothing quite like a fair fight.
[...]