Are there times when you sing at the top of your voice while in the bathroom?  

I am definitely a bathroom singer lol. I feel more confident singing there because it is more private. You do not have to worry about stage fright as well lol. If there's no one around, I'd surely sing at the top of my voice, well just to break the silence lol.

yes, especially with the very first drop of the cold water from the shower, hahaha. i often times sing to the top of my voice but in occasions where i am made to do it, never had i let my voice out in singing. it is confusing why i get to sing so nicely (hahaha) while in the bathroom ... might be because of the cold water or my ability to compete with the rushing sounds of the shower, hahaha. and, here is another thing. when i start to sing and my daughter is inside too, she also sings the same song and vice versa. why do we tend to copy each other's song? funny, but we do it most of the time. hahaha

Yes I often sing out loud inside the bathroom while showering especially during cold mornings when the water comes out from the faucet really cold. LOL I don't know but it seems the coldness will lessen when you sing out loud.
I had an experience when I went to Baguio City and the water was really cold and I heard the people in the bathrooms shouting while others are singing at the top of their voices. Really funny but the singing out loud is nice to hear.