A woman who has Asperger's syndrome was "forcibly removed" from a screening of her favourite film by cinema security staff for "laughing too much".
Tamsin Parker, 25, had been watching western The Good, The Bad and The Ugly at the British Film Institute (BFI) on London's Southbank on Sunday.
Many cinema-goers walked out in protest at the "disgusting" way she was treated by some audience members and staff.
The BFI has apologised and said it "must do better".
Lydia Parker, Tamsin's mother, said her daughter - who was celebrating her 25th birthday - was in "floods of tears" when she picked her up from the security office.
She said she was "shocked and disgusted" about the way Tamsin was "humiliated".
"There's clearly a huge lack of awareness about people with autism," Mrs Parker added.
She said her daughter, who is an animator, had been "so excited" about the screening.
The 1966 film means a lot because, as Ms Parker explained in a video she produced, she identifies with one of the characters.
Am shaking with anger. That poor, poor woman. Just a little bit of empathy and everything would have been fine. Such naked intolerance. In the middle of London. Disgusting.— Lloyd Shepherd (@lloydshep) April 29, 2018
Lloyd Shepherd, 51, who was at the screening with his son, said Ms Parker laughed very loudly at the "amusing bits" of the film but that it was never "inappropriate".
The novelist said some audience members began getting "uptight" about the noise and spoke to staff.
He said one man then shouted abuse at Ms Parker, who was with two friends.
Mr Shepherd said security staff "dragged" Ms Parker out, as she told the audience: "I'm sorry, I've got Asperger's."
Asperger's is a form of autism and people with the syndrome can find social relationships and communication difficult.
Ms Parker, from Cricklewood, north-west London, was "incredibly upset", Mr Shepherd said.
He added: "People were applauding the guy who abused her, and they applauded when security took her out.
"Those people need to take a long hard look at themselves in the mirror."
I waa there too and found it sickening. A very unfortunate and uncomfortable situation. I would like to say that having returned later after calming down, I spoke to the manager and believe she was in a very difficult situation, still 100% not fair what happened to that lady.— Rich (@Richlegate) April 29, 2018
It was shocking to witness. The abuse she received for simply laughing and enjoying the film. It broke my heart to see this unfold. My son was with me, he is autistic too, we went to try &make sure she had a safe space and that staff knew how to support her. I hope she is okay x— Lindsey Ilsley (@LindseyIlsley) April 30, 2018
Please wish her a happy birthday from me! Her excited whoops before the film began got me excited to see it for the first time! Wish I’d been brave enough to whoop with her— Johnny Ellis - Talent of Are You Movie Mad? (@movie_mad) April 29, 2018
The BFI said it was "sincerely sorry" and would look into training staff to be more sensitive.
In a statement, it added: "In what was a challenging and complex situation, we got it wrong.
"We can and must do better in accommodating all the needs of our customers."
Mrs Parker said security staff were "sympathetic" once they realised her daughter had Asperger's.
But she said her daughter "shouldn't have to check in" with staff in order to avoid such a "horrible experience".
Jane Harris, from the National Autistic Society, said she was "shocked", adding: "With over 700,000 autistic people in the UK, it's vital that they are able to enjoy going to the cinema just like everyone else."