#3. The 'punching bag' is a boxers' item used to help them practise/master their punching techniques. So this is quite gross -- it could imply that the person enjoys hurting another person (his scapegoat) either physically or metaphorically.
Have a look at this link:
Punching bag - Idiom Definition - UsingEnglish.com
#1 'The point of no return' is usually used to describe that you can't go back and must continue on your current course. The whole sentence is not quite clear to me though.
Student or Learner