Mrskipling My sister's attitude was the same as yours. It was in the 80s, she had been cycling around central London for 20 years or more without incident, she also had big hair and did not want to crush it with a helmet.
But one day a lorry came up to a T junction in a quiet part of central London. It was a tree lined road, lined with parked cars, which entirely hid her from the lorry driver. He was turning right, very slowly, so as he came out he was looking left for traffic from that direction and did not see the cyclist on his right. His lorry just clipped her rear wheel. She fell off and cracked her head on the curb and died three days later.
You may say 'Well I will be dead' so it doesn't matter. Have you thought what effect your death or lifetime with a severe brain injury of other disability will be like for your family?
The devastation and pain my my dear sister's death caused can still be felt by family members 30 years after the event, and worst of all their knowledge that she had been warned this could happen if she did not wear a helmet.
How much can you really care for your family if knowing the devastation an accident like this could inflict on them - and you must know - you still will not wear a helmet.