I have a brother who always sing in the bathroom, singing in the bath, or singing in the shower, is a widespread phenomenon.
I cannot carry a tune so I do not do that.  I wonder why people do that.
Bathroom singing
Bathroom singing, also known as singing in the bathroom, singing in the bath, or singing in the shower, is a widespread phenomenon. 
Many people sing in the bathroom because the hard wall surfaces, often tiles or wooden panels, and lack of soft furnishings, create an aurally pleasing acoustic environment. The multiple reflections from walls enrich the sound of one's voice. Small dimensions and hard surfaces of a typical bathroom produce various kinds of standing waves, reverberation and echoes, giving the voice "fullness
Mr Barrington is wonderful. He always manages to sing one-sixteenth of a tone flat; it's so like a vicar." Barrington went on to say that producer Richard D'Oyly Carte later came to see him, saying, "...what's the matter? ...some one has just come out of the stalls to tell me you are singing in tune. It will never do." Barrington said that "This pleased me so much that I have never sung flat since, except, of course, when I