When you punch yourself in the balls as hard as you can to kill the sperm right before you ejaculate into a woman's vagina as to avoid other forms of birth control.
"Wow, the punching bag I gave myself last night hurt, but not as bad as 18 years of child support would have."
A lazy way in which Teachers are indulging bullying to maintain "discipline" . A designated punching bag is a student on whom the Teachers are counting to always be the ones bullies will target to pass their "hormonal" energy while leaving teachers favorite students alone. That becomes the "natural order" and routine for teachers. If the Designated punching bag get fed up and fight back...or only wants to save his/her neck, he/she breaks the teacher's routine and natural order therefore HE/SHE is committing an infraction in the eyes of those teachers.
Student A was stolen, beaten up etc... One day he had enough and fought back. But since for teachers he is the school's designated punching bag, he was expulsed because HE and ONLY HE (not the bullies) has to learn how to behave in Society!
n. The act of taking a used condom, tying it at the end (resembling a real punching bag), and pummelling one's parter in the face with it until it breaks and the semen inside explodes on her face.
In exchange for a rowdy round of sex, John gave Betsy the punching bag.