What if instead of roaming the streets of New York in his yellow taxicab, Travis Bickle cruised LA behind the wheel of an Uber listening to bad techno? That’s more or less the gist of this silly and slightly tedious serial-killer black comedy, a satire on social media that’s as subtle as Donald Trump’s Twitter account.

Stranger Things actor Joe Keery appears to have prepped for the lead role by guzzling energy drinks by the crate-full. He is Kurt Kunkle, a relentlessly upbeat 23-year-old who has been trying to make it as a social media influencer for the past decade. But viewing figures for @kurtsworld96 remain stubbornly in single digits. So Kurt has found employment in the gig economy, working as a driver for a taxi hailing app called Spree. Which gives him the idea for some “fresh content” for Instagram: live-streaming himself murdering passengers (his victims include Mischa Barton) by poisoning bottles of mineral water given out free to customers.

But humiliatingly for Kurt, even his murders fail to trend: “ur shit is awkward and boring.” So he ups the ante, going viral with some nasty 18-certificate deaths, one involving a drill, another savage security dogs. Director Eugene Kotlyarenko shoots in a style that might be described as found footage 2.0 – filming as if on the characters’ smartphones, their followers’ comments popping up on screen. It works up to a point, but he doesn’t have a way with filming violence; the grisly murders here are neither scary nor funny. And there is little to explain what turned Kurt into a homicidal maniac, other than one of his passengers calling him a “loser incel”. Keery is a likable actor, nicely cast, but his one-note, perky performance doesn’t help. Spree is meant to comment on the shallowness of social media culture; the trouble is, it’s a film with the depth of a puddle.

• Spree is released in UK cinemas on 14 August.