Rating: The director of Dirty Grandpa, Dan Mazer, came on stage before the UK press screening of his latest comedy, as is customary, to give a little speech selling the movie. He opened with, "I'm aware you had better things to do tonight." Joke's on him - I didn't, but he was still right. Dirty Grandpa is made with the full awareness that it isn't funny. It makes an endless stream of faux outrageous gags (sometimes the same ones repeated from half an hour before) in the lethargic belief that overwhelming quantity can make up for a dearth of quality. By the sheer law of averages there are a couple of giggle-worthy moments, but the movie is as surprised as you are when they do; whereas a good, self-assured comedy would typically edit in natural pauses between jokes to allow time for audiences to laugh, here the film just ploughs on regardless as it knows 90% of them are going to fall flat anyway. In some ways it's admirable to see a film almost admit it exists entirely for the benefit of teenagers wanting to guffaw at lewd jokes (cancer gags are treated like petty change); there's a simplicity to the focus and the lack of pretence in trying to be anything more is nothing if not refreshing. But I don't think knowing you're going for the lowest common denominator should be an excuse for making a bad movie. As the lip-sync fails pile up, it's hard to escape the feeling that the film is the way it is because Mazer had "better things to do" during production. What really wears thin is the appalling sense of character. At the start Zac Efron is meant to be a stuck up lawyer yet can't get his tongue around any jargon, while the vulgar nature of Robert De Niro's grandfather never comes across as particularly shocking because there's no attempt to ever make him look like a saintly papa in contrast. By the end I just gave up trying to rationalise all the bizarre, thoughtless plot decisions; the third act works only if you accept the characters aren't real, merely caricatures that are aware they're in a narrative that must be wrapped up in 102 minutes. I don't want to be the guy to muse on the downward spiral of De Niro's career - it's been a spent observation since Rocky And Bullwinkle (oh yeah Bob, I remember) and I do like his recent work with David O Russell - but the film almost begs it. The opening credits are full of photoshopped images of a young De Niro and the whole thing's about growing old and enjoying your twilight years. There's even a diner scene early on that's trying to invoke a climactic scene of Goodfellas - no doubt intended to trick cinephilles into thinking it's "smart" - which almost mocks his descent. Now I will give it to the two-time Oscar-winner - he is having fun here, and the jokes that do land come from him. And that's what's so worrying; if he does care, he's moved on from doing things for the money and now legitimately doesn't give a sh*t what people think. Oh well, at least I can strike "See Robert De Niro wanking" off my bucket list. Sigh. Dirty Grandpa is in US cinemas now and UK cinemas from 28th January (previews from 25th January).