Noun
an inflated ball or bag that is suspended and punched for training in boxing
a person on whom another person vents their anger
Source: WordNetI'm not going to be anybody's punching bag. Tim Kaine
You punch me, I punch back. I do not believe it's good for ones self-respect to be a punching bag. Ed Koch
What happened to you? (Sin) Was mistaken for a punching bag again. But what the hell, I'm used to it. (Xypher) Sherrilyn Kenyon
he resigned because his boss used him as a punching bag Source: Internet
And, as if you didn’t know already, his next two games are against the foreseeable punching bag of group D: Midtjylland. Source: Internet
A punching bag in the middle of the ring was used by De Niro between takes before he aggressively came straight on to do the next scene. Source: Internet