The truth of the matter is that Anders is writing lyrics for a certain audience, most of which are, yes, high schoolers and edgy college students. He is speaking their language because they think it's cool. He is dealing with the subject matter that they find interesting and relatable. That's In Flames' current audience. Obviously the older fans aren't receptive to this, but that's not who In Flames is engaging with these days.
I saw a post on their official Twitter account a while back asking what fans' favorite songs from Battles were. All positive comments, mostly from younger people, all enthusiastic about Battles. "Drained" was In Flames "bringing the metal back!" Seems silly to us, but this a different audience, and times have changed.
Doesn't mean you can't laugh at it, but I don't see why anyone is surprised.
I would say that the chances that they're the result of him being deranged or malicious are fairly low.