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1.
A phenomenon in which an occupant of an upstairs bathroom is unable to hear what individuals downstairs are yelling up to him.
Marie: (To Kenneth) Darling, your brother is on the telephone!
SILENCE
Matthew: Alas, dear; he is using the upstairs bathroom and is thus unable to hear that which you are attempting to communicate to him. He may as well be deaf. This is a superb example of the so-called upstairs bathroom effect.
by Tyler the Definer June 05, 2013