Keep in mind that I started recording the material about halfway through. (I skimmed the first half, but may have missed some things.)
religious exclamations - minor (46) - major (4)
multiple uses of s*cks, pr*ck, slut, b*st*rd
Teenage girls joke/insinuate about size of boy's privates
The 17-year-old Miranda plans to have sex with her boyfriend (her friends push her to it)
At one point they kiss, remove their shirts, and continue kissing on top of each other.
Later in the book she sleeps with her other love interest. (Although the scene is only implied.)
A cab driver gets shot with blood spattering on a car window. Various others get shot or are heard screaming from apparent torture. The idea of kids getting tortured could be very disturbing to some readers. Miranda gets tortured in great detail. (Electrocuted and fingers broken.) One person commits suicide by shooting themselves in the mouth.
The idea fact that they go back in time to kill a seventeen-year-old boy who will one day become a murderer may be disturbing for many readers. (Although they don't end up killing him, he does off himself, which is also quite disturbing.)
General disrespect for parents: Miranda has a very poor relationship with her mom and dad. She pretty much hates them and they seem to care very little for her. Miranda's friend calls them "a**h*les."
Things kids might emulate:
Unmarried sex and underage drinking are portrayed as glamorous and consequence free.