The prank took place at the Vue cinema in Worcester (UK) on Friday, less than 24 hours after the massacre at a cinema hall in Aurora, Colorado, screening 'The Dark Knight Rises', in which 12 people were killed and 59 injured by a masked man.
The stunt has been condemned by "appalled and sickened" audience members who have written to Vue demanding an apology, the Daily Mail reported.
Schoolteacher Elizabeth Atkinson was at the screening with brothers James and Leo.
"In light of the recent and tragic event during the screening of the new Batman film in Aurora, Colorado, I was shocked and appalled by the attitude displayed by the staff at the Vue cinema here in Worcester," she said.
"While the trailers were in progress, one of the cinema attendants entered the screen room wearing a gas mask and stood to the side looking at the audience. This is exactly as the gunman in Colorado was reported to have been dressed," she added.
"I was not the only one who found this to be extremely disconcerting and inappropriate. I raised my concerns to other staff members outside, explaining that this attendant was causing discomfort," Atkinson said.
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"The response I received was one to suggest that they were either unaware of the recent shooting, or they were indifferent to it. I was told simply that he was 'Dressed as the villain, Bane'," she said.
It was only when she explained further that the Colorado gunman was also dressed in this way, that the attendant was spoken to and the mask removed.
Her brother James has written a letter of complaint to Vue.
Mr Atkinson, a freelance film maker, wrote "Even though I knew he was meant to be dressed as the character Bane from the film, I felt it was incredibly insensitive indeed in light of the recent shootings in America by a man wearing a gas mask."
A spokesman for Vue cinemas was not able to offer an explanation but said "Everyone at Vue Entertainment is deeply shocked and saddened by the tragic incident that took place in Denver over in the United States."
James Holmes, 24, is accused of the deadly attack in the US.