Quaking in the boots - It simply means a degree of fear and terror or simply fear in one's behaviour at a given time.
1. He was quaking in the books when he heard those bullets being fired near his house.
2. I don't understand why he does not quake in his boots even when he saw the snake, really macho.
3. Matt was quaking in the boots when he saw his father coming, while he was talking to his girlfriend.