That's pretty poor evidence. While I do wear a helmet, having read a fair bit of research on the subject I would hardly rate someone who chooses not to as dim and stubborn - certainly no more so than someone who opts to walk without a helmet, and far less dim and stubborn than someone who takes the risk of driving without a helmet.

Which isn't to say that your coworker specifically isn't those things, but the helmet issue is hardly evidence of such.

The mirror strikes me as a more productive safety feature, though I can't say I've done any research at all on that subject.