Clue: Bad-mannered son twice sent back to hospital (7)
Answer: YOBBISH
Explanation: Definition: Bad-mannered

**<=(SIB BOY)** ("son",* twice sent back*) *to* **H** (hospital)
 

 
*Not convinced by "sib" = son, as the status of being a sib relies on having a brother or a sister, rather than a parent.