When a film comedy goes wrong, the one-liners drop like stones, the jokes sail wide of the mark, and time moves so slowly that it’s almost like being stuck in a bullet-time sequence from The Matrix. Get Hard slides gloomily into the latter category. It’s the kind of back-of-a-Spar receipt low concept that would struggle to fill a 25-minute sitcom episode, yet Etan Cohen (the Idiocracy and Tropic Thunder writer who makes his directorial debut here) attempts to extend it to an hour and 40 minutes. Now, there wouldn’t necessarily be a problem with this if the jokes were honed like a shiv. There are plenty of comedies which thrive on virtually no plot at all; Withnail & I managed to string an hilarious yarn from a story about two men going on holiday by mistake. But Get Hard bobs along on a depressing sea of jokes about genitals and posteriors – and worse, these are the kind of semi-improvised genital and posterior jokes which would barely pass muster in a school locker room. Will Ferrell is part of the problem; he’s woefully miscast as the pompous rich guy set up for a fall. Ferrell sits in front of computers and talks about stocks and shares, or makes references to classical Greek literature, but it’s impossible for one moment to believe that he’s a hard-nosed, expensively-educated Wall Street guy – Patrick Bateman wouldn’t even hand this chump a business card. The James King role needs somebody urbane and poised – to paraphrase Krusty the Clown, “The pie gag’s only funny when the sap’s got dignity”. Ferrell should be playing the straight man, a part that would probably have been better served by a respected actor with a willingness to send up his own image – two of the names we came up with in the taxi home were Tom Hiddleston or Benedict Cumberbatch.  Make no mistake, Kevin Hart is the single best thing about Get Hard. He’s likeable, generous on screen and funny without making his presence hectoring. One of the funniest scenes – perhaps the only truly laugh-out-loud moment in the entire movie – is one where Hart insists to his wife, Rita (Edwina Findley Dickerson) that he can convince James King he’s a tough ex-convict (one of the film’s running gags is that King assumes that Darnell’s been to prison simply because he’s black). Hart’s frustrated outburst provokes a furious response from Rita – and the moment’s so perfectly played by both actors that it leaps from the screen where other gags simply come and go with an apologetic shrug. It’s a rare oasis of inspiration in a creative desert. Cohen’s direction is flat at best; the camera lingers uncomfortably on long and unfunny scenes of (presumably) improvised trash talk, while a potentially decent moment of anarchy, involving farmyard animals, a wine cellar and a set of improvised weapons, dissolves into a sludge of unwatchable strobing effects. Get Hard is out in UK cinemas on the 27th March. Follow our Twitter feed for faster news and bad jokes right here. And be our Facebook chum here.