The actors portrayal of Cal + Andre's personality.
The actors portraying Cal and Andre did an ok job making u believe the realness of their character; in other words their acting seemed "natural".
But what i didn't see were those tell-tale signs/personality traits of a mentally disturbed, homicidal and anti-social serial killer-to-be (esp when they've been planning it for over 6months).. I don't know they just seemed like your average NAIVE, SELF-CENTERED run of the mill maybe nerdy, and unpopular/awkward teenagers.
I don't get if they were supposed to be portrayed as "normal" as possible by the actors because nothing screaming "PSYCHO!!!" was gotten from their 1.5hrs of screen time.. An exception being Cal's prom date saying Andre was a psycho, but nothing else.