You have to pick:

Umm... That's evil. If you forget that you can't say chair, you could very easily causally say it when asked a related question.
I would have a hard time remembering I couldn't say chair.

And what if I become suicidal briefly. It would be so easy to say chair and be done with it, compare to other means witch might turn me off to doing the act...

And not saying chair might drive me so crazy I'd say it...

Or worst yet, you don't know this ahead of time, so next time you say 'Go grab a chair...' you drop dead?

This is a good one.

What if your deepest, darkest secret is that you can't say "chair" without dying? And then your enemies try to make you say "chair".