What is the issur on making a bracha on a cup of coffee & then taking that cup of coffee into the bathroom with you ?
Answer:
This is fine, in particular for a bathroom with a shower etc.
For the status of bathrooms today see here, and this is all the more relevant for the matter of taking a cup of coffee into a bathroom (as opposed to the stricter question of reciting a berachah in a bathroom and so on).
Best wishes.
