Nobody ever admits they do their best writing in the bathroom.
(Being genteel, there's no need to elaborate on activities beyond the work.)
Bathroom writing is the closest to being in some kind of Paddy Chayefsky 'Altered State' isolation chamber. Characters there exist fully realized and unashamed, bounding about the walls and toothbrushes like the freed Neanderthal living inside all of us. It's quiet in the bathroom until people begin to look for you, and even then you're safe from interruption (assuming you live in a 2-bath domicile) because you're in a bathroom. What kind of lowlife scum is going to burst in and risk that kind of emotional scarring? Granted that writing is a hobo's activity--and my hobo pack of tools travels extensively (mostly pen--I am the last person in America without a laptop, owing to the fact that I'm pretty much broke—send your gently used laptop to…)--but the pristine clarity of bathroom thoughts (different from and yet somehow the same as just-woke-up thoughts) means that, should my writing ever take off, my first dedication will properly thank Johnny On The Spot first, my wife second, and my highly tolerant Muse goddess third. I would love to write in my office but as that generally surreptitiously occurs at work, I make do with the small, quiet space outside my bedroom that welcomes me—with cottony softness, no less--pretty much every day.