When we think of basically the three types of ignorance, we could say in the mind, we have greed, wanting, wanting, wanting; we have got aversion, not wanting, not wanting; and we have ignorance, or delusion. We just don't know, we are deluded. Delusion does use up your good Kamma.
So, driving a motorcycle when you know you should wear a helmet but you don't, is part of being deluded. Greed could also be involved with the delusion. That lovely feeling of the wind in your hair, the wind on your face and that feeling of flying through the air. Take it for all you want if you ever drive a motorcycle without a helmet. If I was in the situation of driving a motorcycle without a helmet when I was 32 or so, I would not have my jaw right now, or it would have been rebuilt because it would have been smashed. I had a motorcycle accident, I went down face first. My helmet was a full face helmet with a bar across the bottom. When I stood up the bar was all scratched across the bottom. It was a solid helmet, I didn't break anything, my ankle got damaged, my knee got damaged, but my jaw was safe. So not using a helmet in those types of situations is a delusion, it is an ignorant type of state of mind which does not respect Dukkha, does not respect the possibilities of accidents and so on. So yes, as to my understanding, it is wasting good Kamma.
Now, on the other hand, I would like to make a comment on a person who is a very fast and risky driver and has no accident, for those who are here now, maybe you have been risky before, maybe you have been fast, maybe you haven't had accidents. But do you really want to live that way? This is where the Compassion has to open up more. Open up to be more careful. We don't really want to take all those risks. We don't really want to have accidents unnecessarily, what is the point? We don't want to risk throwing away a good opportunity to be a Dhamma practitioner.