I’ve had a lot of CRAY experiences on the subway. No really, I actually keep a slightly embarrassing Harriet the Spy-style blog about it (#shamelesspromotion). But I’ve yet to see a spontaneous and unintentional Rihanna concert performed by a young, shaded guy with headphones on.
In situations like these, it’s best to avoid eye contact, unless you’re really into the song and want to sing with him, but that’s not recommended. Your response to his off-key singing can be difficult because your knee-jerk reaction is probably to laugh until you cry. I advise you to step back as far as you can while still remaining in hearing distance (you don’t want to miss the show), pretend to pay attention to your book and then keep a poker face.