Before we begin, we need to make something perfectly clear. Our back-end system doesn't allow us to give zero stars for... a load of technical reasons we're not going to bore you with. That star-rating you see above the review? That should be a zero. This is a zero star-rated film. There is nothing redeemable about this. Nothing. Everyone who worked on this, from the person who did the lighting to Robert DeNiro, should be ashamed of themselves. Every single one of them.

Let's start with the plot. It's the most basic, by-the-numbers, unimaginative plot. You could write this on the back of a toilet tissue covered in constipated shit and it'd make more sense. Zac Efron is an uptight lawyer who's about to get married to an equally uptight blonde lawyer. His grandfather, Robert DeNiro, has just buried his wife and had planned his annual trip to Boca, Florida. Wanting to honour that tradition, he convinces Zac Efron to come with him. Efron goes to meet DeNiro at his house and finds him naked and masturbating to porn. After a game of golf that involves DeNiro forcing himself on a couple of older women - sorry, cougars, as he refers to them - they set off for Boca.

They stop off at a cafe and, miraculously, a former college friend of Efron's, Zoey Deutch, is there at the same cafe and remembers Efron. He wanted to be a photographer, but his father, Dermot Mulroney, convinced him to go into the law business. With Zoey Deutch is Aubrey Plaza, who likes to have sex with old-age pensioners, and Jeffrey Bower-Chapman, who plays a gay stereotype. The film then goes through motions - Zac Efron smokes crack, Robert DeNiro beats up various gang members, Aubrey Plaza makes sex jokes - before it ends with Aubrey Plaza stripping down to her underwear and asking Robert DeNiro to say various OAP things like, "I can't find my glasses!" and "Tear me open like a Social Security Cheque."

Now, at this stage, you're probably thinking the reason this is a zero-star rating film is because it's highly offensive and low-brow humour. You're partially correct. The other reason is that it's all of those things and still not funny. In fact, it's heavily relying on shock value to make you laugh. It doesn't. At all. It's trying so desperately to be funny that it just comes off as, well, desperate. This film is about as funny as a badly-misspelled meme pulled from a shady-looking Facebook page. The jokes are fired off regularly, but nothing sticks and you eventually just resign yourself to the fact that this is a waste of money. We can't stress this point enough. Do not pay money for this film. By handing over your hard-earned money for this shit, you're propagating it. You have a responsibility not to watch this because if you do, you're funding the next one.

Let's look at Robert DeNiro. Arguably the greatest film actor of his generation. 'Goodfellas'. 'Casino'. 'Heat'. 'Awakenings'. 'Midnight Run'. This film is Robert DeNiro gathering together his life's work, throwing lighter fluid over them, setting it all on fire and then pissing on the ashes whilst making rape jokes. Robert DeNiro is no longer the greatest film actor of his generation now. The rot started with 'Meet The Parents' and now, it's metastasized into this. There is no coming back from this for him. Zac Efron, fine, he's young, his best work - if you can call it that - is ahead of him. But DeNiro? He's thrown it away on a pay-cheque and, presumably, funding for his Tribeca Film Festival. Sure, he's done his serious work and now he wants to take the money and have some fun. If that's the case, he could have kept doing crap animated films like Shark Tale and still made money for his own projects. No, here, he made a choice. He must have looked at this script, thought "Yeah, I can do this," and signed on the dotted line and collected his money. He has to be held accountable for that choice.

Director Dan Mazer began his career on the 'Ali G Show', a hilarious, well-produced satirical show that stuck its nose up at just about everyone. It thrived on being offensive and the writing was so smart, so clever, that you almost didn't realise it. Can he be held responsible here for this? Yes, definitely. This is John Phillips' first screenplay and his next one will be 'Bad Santa 2'. Let that sink in for a minute. He's working on the sequel to one of the best comedies of the last ten years. They're letting him near that. Fantastic stuff. Well done.

'Dirty Grandpa' is officially the Worst Film of 2016 so far. Do not spend your money on this film. Don't rent it. Don't stream it. Just don't. And don't go see it for curiosity factor, either. It's not worth paying out whatever your cinema is charging. Go see any other film that's in the cinema. Really. And if there's nothing on at that time, wait for something to come up. Go for a drink or something in the cinema's bar, if it has one. Do not watch this film. You'll regret it.