Exactly how steamy is this story?
PG-13
Sex is definitely a thing that happens in Please Ignore Vera Dietz. Vera and Charlie are teenagers after all, and they've got some very hormonal urges. Charlie ends up with Jenny Flick largely in part because she's easy (as bad of a motivator as that is). He's just excited to have a girl around who will sleep with him, even if she does turn out to be a pathological liar and a huge schemer.
And then there's the whole creepy pervert storyline. When Vera and Charlie are just kids, this guy shows up in a white car and offers them money to let him take pictures of them. We're going to go out on a limb and guess that these aren't just innocent photos. Charlie ends up selling his used underwear to the guy, and eventually even lets him take pictures of him and Jenny Flick doing… stuff.
Even though those are some serious sexual themes in the book, it's still at PG-13 because the reader doesn't actually see any of these things happen. We just get the watered down mentions of them.