I know what you go through with people like that. My reply often ends up along the line of this;Coworker - "Are you nuts!? Do you have a death wish!? You're nearly 60 you shouldn't be doing this! Now, he's beaking off at the office how nuts I am. I really want to plow him but of course I can't. I didn't know what to say.
"Listen, I know that me riding a motorcycle scares you. I understand completely. I have two cats at home. One is a outdoor cat and the other is a indoor cat. The indoor cat thinks the other one is totally insane for going out there."