I don't think is it polite at all. I think it is very rude. even if your visting someone for few hours and take a big poo in there house that might or might not make a big smell. Even if it is a guess Loo.
I think it is ok if your staying the night. Or you have a medical condition. but even then I would try to avoid having a poo.
I think if someone offers you the loo. I don't think it gives you the right to do everthing you feel like in their loo. A Pee and wash hands is the correct thing to do and out of respect for your friend house. But nothing more and shows good manners.









