a Blow
When two people punch each other like they're in a cage match, but with more humiliation.
You punch me, I punch you, and we both end up with a black eye and a bruised ego. That was blow for blow.
He took my lunch money, I took his pencil, and we ended up in the principal's office. That was blow for blow.
She said I was ugly, I called her a f***ing meatball, and we both got suspended. That was blow for blow.