I lost a friend in a car accident too because he didn't wear a seat belt and I don't start driving until everyone in my car wears one. One time I drove 3 friends who were friends with the one who died too and they refused to wear a seatbelt. I argued for a few minutes and when they still played it down as me being "overly cautious" because "we only drive less than a kilometer" I said "Ok", started driving, accellarated to 30km/h and stepped down on the break as hard as I could. They smashed into the front seats, the one in the passenger seat even knocked his head on the windshield. I told them to put their effing seatbelts on, otherwise I would be happy to see what will happen at 50 km/h. I don't understand why but they rejected the offer and finally put their seatbelt on. After that I never needed to remind them again.