Punishment or payback rendered at the hands of a vigilante or any other punishments given outside of official channels. Often times the punishment is illegal and excessive for the violation.
Linda parked her car in my spot for the 3rd time this month; I handed out a little street justice by slashing her tires.
An act or state where a Person A does something minorly offensive to Person B, and Person B retaliates by doing something much worse in degree to Person B so that Person A will never choose to mess around again with Person B.
In other words: when someone wrongs you and you do something way worse back to make sure they don't fuck with you again.
1. That fool scratched Jim's car so Jim had sex with the fool's mom; now that's street justice.
2. That guy made fun of my brother, so I broke both his shins. Street justice, man.
Illegal procedures, especially to get things done.
Why most cops use street justice?