In the 1999 rom-com, the actor played bumbling book store owner William Thacker who falls in love with a movie star played by Julia Roberts but Grant has labelled him "despicable" for the way he treated the actress throughout the movie.
Speaking as part of Vanity Fair's Scene Selection, Grant explained: "Whenever I'm flicking the channels at home after a few drinks and this comes up, I just think, 'Why doesn't my character have any balls?'
"There's a scene in this film where she's in my house and the paps come to the front door and ring the bell and I think I just let her go past me and open the door. That's awful."
Grant went on to insist all his real life romantic partners had the same opinion of the character, saying: "I've never had a girlfriend, or indeed now wife, who hasn't said, 'Why the hell didn't you stop her? What's wrong with you?'
"And I don't really have an answer to that - it's how it was written. And I think he's despicable, really."
He added of his co-star: "Probably all the time with Julia, as with any brilliant actress, you're just thinking: 'Christ, they're really good. I'm not going to be as good as her'.
"And she's great at emoting and she's got this kind of quality where it looks like her skin is wafer thin. You can sort of see her soul."
Grant has previously cleared up reports suggesting he hated all of his film roles, insisting he just picks holes in his past performances.
He told The Hollywood Reporter: "I've read that I hate all my films. That's not true, the films are often great. It's just me that I loathe.
"I always think, 'Oh you f***** that up'. You never feel great about your own stuff. It's like in the old days of answering machine messages you always felt nauseated when you heard your own voice. And watching yourself on film is that times 50."
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