Should one repeat after the muezzin while in the restroom (may Allah honor you)?

It is disliked to mention Allah Almighty when relieving oneself, out of veneration for Allah's name. This includes all forms of remembrance (dhikr) and speech, except for speech necessitated by need, and repeating the adhan. This dislike is one of tanzih (disapproval without prohibition), not tahrim (prohibition). As for dhikr performed by the heart without moving the tongue, it is not disliked.