I've been a massive fan of fast-talking bullshit artist Vince Vaughn since his Swingers days, and I had an embarrassing crush on Rachel in Friends – or on Jennifer Aniston, more likely, since every role she plays is exactly the same. I love both leads, and detested this film, so I can only wonder what those less well-disposed towards them think of this appallingly poorly-judged attempt at romantic comedy – the first I've ever seen without even an attempt at romance.

Vaughn and Aniston as a couple is just as implausible a concept onscreen as it is when you see them cuddling in NW. And, as in real life, all we have to prove it are photos of the two together, which play under the opening titles. The chemistry between them – the fuel of any romantic comedy – is left to a corny opening scene in which Vaughn unsuccessfully fails to straddle the precarious line between being charmingly forward and a stalker. Not a promising start.

The rest of the movie is post-break up. It's a bold, original approach, and perhaps with a better script and casting, it might have worked. The pair are still in love, and too proud to admit it. Contrivedly, neither's willing to move out of their dream condo, leading to many a ding-dong battle as Aniston's character attempts to win Vaughn back – though why on earth she'd want to eludes me – by dating other men in the hope she'll get some appreciation.

This strategy may explain why she dated Vaughn in real life as well. Sadly for her, though, Brad failed to notice. I hope for Jen's sake that the audiences prove equally resistant yet another failed comic turn by Hollywood's most inexplicably sought-after actress.

The film's attempts at humour generally misfire badly, as you'd expect from such a contrived premise. The comic moments are either too over the top to be funny or just sad. The film's biggest comedy set-piece, where Aniston's brother tries to get an entire dinner party to join in a highly effeminate a capella performance, tries far too hard, and doesn't have a laugh in it. The supposed gross-out scenes, like Vaughn's wild frat party with strippers, just make Vaughn look like a loser. The romantically awkward moments where Aniston's other men fail to make Vince jealous feel wrong, and the scene where he turns up to bowl and is rejected by everyone just made me wince.

But even more problematic than the firm's attempts to be funny are its attempts to be serious. It's constantly shifting gears down to completely depressing, such as in a harrowing scene where the counselling breaks down, and in particular the final moments of confrontation. Unlike the supposed comic scenes, these do ring awfully true, even if the acting and attempts to play them for laughs don't. These moments of pure relationship anguish would have deflated any notion that this might be a comedy if the ham-fisted comic writing hadn't gotten there first.

Since Aniston had just broken up with Brad Pitt when the film was made, it's remarkable how little pathos she's able to bring to her emotional scenes – surely conjuring real tears wasn't too hard while Brad was gallivanting around impregnating Angelina Jolie? The relentless media coverage had me tearing what's left of my hair out in frustration, and I wasn't dumped by the hottest man in Hollywood.

If the real-world evidence hadn't been so ubiquitous, I don't think I would have believed that Aniston and Vaughn had hooked up during filming. Their chemistry here is as defective as an ecstasy tablet cut with horse tranquilliser. Which pretty much describes what it's like to watch this film. If you leave out the ecstasy part.