How about I tell my husband he is absolutely not allowed to get a motorcycle?
Why would you say no to something that brings him joy?
Because if he gets the bike he will start acting like he's king of the road and that worries me.
It sounds like the bike might make you nervous, which is understandable. It is good that you are concerned about the safety concerns that come with getting a motorcycle.
Well that and I'm also worried about getting cancer from the fumes and him giving cancer to other people cancer from it. I don't want other people to suffer so I'm just gonna make fun of him so he doesn't want the bike anymore.
It is good of you to care about the safety of others. You shouldn't tease your husband or make him feel bad for wanting something he loves. I would talk to him about how it makes you feel and maybe you can compromise.