Evan, a nerdy high school senior with severe social-anxiety disorder (Ben Platt), is tasked by his therapist to write motivational letters to himself as a way to improve his disposition and communication skills. One such letter is stolen by a troubled classmate who subsequently commits suicide, and the discovered letter is mistaken for proof that the noted bully had at least one friend.

Evan is summoned to meet the guy’s family but is unable to tell them the truth and even elaborates on what a great guy he was. Fueled by today’s social media mania, the lie and the self-created dilemma keep growing, to the point where Evan needs to come clean and learn life lessons, yada yada.

Just makes you want to sing about it, right? My first reaction, five minutes in, was, “Oh fudge” (okay, not the precise expletive), “It’s a musical.” For this is based on the hit Broadway musical, which I understand took home several Tonys and a few Grammies. So I recommend you try to catch a stage performance or buy the soundtrack. But the only people that should actually watch Stephen Chobosky’s tone-deaf adaptation are film school students wanting a lesson on how NOT to adapt a play. This is the rare disaster that even Amy Adams and Julianne Moore can’t save.

The first of Chobosky’s maudlin missteps is to retain Platt in the title role. Granted he is a uniquely talented vocalist, but he’s pushing 30 now, and while I realize the role calls for a certain cluelessness, the charismatically challenged actor is merely annoying. Especially when he’s lusting after young Katilyn Dever. Plus he’s in almost every scene. The director has excised a few songs, but also most of the reported humor, and it’s open season on the shameless and cynical emotional button-pushing.

People often ask me if I watch every movie I review all the way through. Yes, I do. But this one was a slog, taking four of five sittings before reaching its end, two and a quarter hours distant. Not even so-bad-it’s-good. (137 min)