7-seaters in Hong Kong are notorious for angry, inconsiderate driving, the pressures of having a family and kids and all.
Taxi drivers can be dicks too, but this one appears to take offence to what seems like some deliberate braking on the part of the 7-seater once it is past the taxi; if so, a deliberate attempt to stick it someone or "troll" them.
After the 7-seater is rammed by the taxi, the driver gets out and verbal sexually assaults the taxi driver's mother, who proceeds to deliver another, purposeful blow.