Rider and pillion (aka girlfriend) are talking to each other at slip road entering into PIE Changi. Rider keep turning his head behind toward girlfriend while having conversation resulting in road hogging and rider keep applying brakes multiple times. Rider is travelling at estimate 15 to 20km/hour leaving a big gap between the rider himself and a heavy vehicle in front. I drove patiently behind the rider and only when it safe to overtake I drove pass slowly. However the angry rider out of a sudden appear beside my car and demand that I stop my car and zip across my vehicle and signal to me to stop at road shoulder and he seem to want a fight. I continue my journey and he zip pass me again dangerously and point middle finger at me. I’m saddened by such behaviour on the road and beseech driver and rider to be vigilant and stay safe.