My freshman year of college, I was submerged into my Music Theory class.
I lived with two sorority girls (don't know how THAT happened), one of whom was nice and the other was...less so.
I have a vivid memory of sitting at my desk, doing my music theory homework, and quietly humming to myself. That's the thing about music theory homework: you need to sing a little bit and probably don't realize you're doing it. (This made finals and midterms especially comical.)
All of a sudden, she yelled, "CAN YOU STOP THAT?!"
I had no idea what she was talking about.
"WHY ARE YOU SINGING?!"
"Oh. Sorry, I was doing my music homework. I didn't realize I was singing."
<<< insert sad face here >>>
In the office now, I am CONSTANTLY humming to myself while my headphones on. I also conduct in the air to nobody. I also play a piano that isn't actually there.
The best part, however, is that when I take off my headphones I hear a whole BUNCH of people quietly humming to themselves (or sometimes not so quietly humming to themselves). You can hear everyone's music blasting from THEIR headphones. You can hear people not using their headphones because they need to test something out loud. You hear people testing the apps out (me included) to make sure things are running properly.
I love it.