she's a good girl with a bad habit

I have been thinking (yes thinking) about some bad habits that people might be keeping from others. one of the most stupid but not very bad but highly annoying habit is that of singing in the shower. I don't know what brings people to do this, because do they think that the walls around them are like some protective barrier, help, in the shower no-one can hear you scream (or sing for that matter). This brings to mind, you never hear of people singing in the bathtub do you..