Singing with headphones

So when I'm walking to class and Jethro Tull's Hymn comes on and that kick ass refrain busts out, what am I supposed to do besides sing along? Really! I generally will keep it on the DL (the down-low, of course) and just hum a little or something, but then...Grateful Dead One Toke over the line comes on and then what am I supposed to do? Or Sum 41's fat lip. That song must be sang along with.
My friend has an idea that I think might be really brilliant. She thinks that everyone should just sing along and not fucking worry about everyone else. Except those people who, like, really sing along and are all good and shit. We don't need to hear that.
Last week I was in the library and it was after midnight on a Tuesday night and there was no one there and I was in the basement. I seriously thought I was alone, so I start singing with my music, and not really all that quietly. I thought I was alone! Then I got up to print something and it turns out there was some graduate student at a computer behind a pole. So I had to leave because I was embarrassed. Asshole.