An 18-year-old with no criminal record is drinking in a bar when a drunken stranger hurls an insult at his girlfriend. After further taunts, the young man hits the stranger, who trips, hits his head on the edge of the bar and dies.

Under the O'Farrell government's proposed new ''one punch'' laws, the alcohol-affected teenager would receive a mandatory minimum sentence of eight years in jail if convicted in court of landing the fatal blow.

But a bikie gang member with a history of violence who lies in wait for a rival gang member and punches him in the face, causing him to crack his head on the pavement and die, would not receive a minimum eight-year sentence unless he was affected by alcohol or drugs at the time.