Alternatively, now might be a good time to put in a fortnight's leave, with the caveat that you expect some kind of resolution to have been reached by the time of your return.

If you really feel that a cow-orker is a threat to your ability to indulge in life, liberty and the pursuit of happiness, then you must voice that. In writing. Not email, not phone.

And, (I know you will anyway but wth) keep it *measured*. Don't want *your* sanity in the balance, too :)