Praise be to Allaah.
Bathrooms are for relieving oneself, not for eating and
drinking, so it is not appropriate for the Muslim to enter them except for
the purpose of relieving himself, and when he enters the bathroom he should
refrain from eating and drinking until he comes out.
If a person eats and drinks inside the bathroom when there is
no need to do so, then he has done something which is contrary to sound
human nature (fitrah).
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked
about the ruling on eating and drinking in the bathroom.
The bathroom is a place for relieving oneself only and one
should not stay there longer than is necessary. Eating or doing other things
there requires staying there for a length of time that is not appropriate.
End quote from Majmoo‘ al-Fataawa, 11/110
And Allah knows best.