I think it would be a very painful and possibly drawn out death, but I think you could do it in such a way that you are guaranteed to die. Off the top of my head, you could drive out to some remote highway in the southwest. somewhere in the mountains, high up and rocky. just drive as fast as you can and crash over a barrier off the side of a mountain. the longer fall the better. wear no helmet and youre likely to die the moment you hit the ground. you may survive the landing with only severe inguries, but if it is a remote enough location, you would probably die of blood loss before anybody could find you. Not a very nice way to go, but It would probablyt work and look like an accident too. you would just have to make sure to have a believable reason to be out there.