Most people think this song is called "You're The Best AROUND", but it isn't. It was originally written for Rocky III (which you learned yesterday) and was also rejected for the movie Flashdance, in favor of Michael Sembello's "Maniac".
That's OK. It suits Daniel-san better anyway. It makes for the perfect fight montage theme song (even if it doesn't completely work in this case lyrically. Just don't listen too closely).
Magically, it also works in this It's Always Sunny In Philadephia montage, where the gang takes a LOT of steroids.