punching bag is a noun meaning "a person on whom another person vents their anger". It carries 2 recorded senses.
a person on whom another person vents their anger
“he resigned because his boss used him as a punching bag”
an inflated ball or bag that is suspended and punched for training in boxing
Definitions, synonyms and semantic relations for punching bag come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.