A hangdog smile的用法和样例：
- After he got out of jail, he always had a hangdog look.
- Mr. B sometimes shows a hangdog look in front of his wife.
- I wanted to tell him off,but he had such a hangdog air I just couldn't do it.
- Tom had a hangdog air about him even though he didn't get caught in the theft.
- Mr. A must have done something terrible because he has a hangdog look today.