"Titanium" by Sia!
Well, this song's all about staying strong no matter what happens, because, well, you are titanium!
I think that this song is to those people who are bullied in some way, because the lyrics say that "all your bullets ricochet," or that all of the mean things that other people say just bounce off of you. Also, Sia has a skin condition, and people always are critical about that, so she may have written this song for those mean bullies who comment about her appearance negatively.
Honestly, I love this song. If I ever feel like giving up on something, or if something's just up with my mood and I'm very negative that day, I just hum this song and I feel better. Works like magic.