Actually, the "raindrops on roses and girls in white dresses" line is a parody of the song "my favorite things" from the musical The Sound of Music. The actual song says those lines and then goes "these are a few of my favorite things." But Panic! Changes it to be "there are NO raindrops on roses and girls in white dresses," lists the horrible things that are and then adds "and a few more of your least favorite things."
this could be a referral to a lot of the people in the song, since they are all doing something they shouldn't and it leaves them in a bad place.