The English language can be a treacherous and slippery thing, with some entirely innocuous words changing their character as they cross the Atlantic. This has sadly been the case with the new movie from M Night Shyamalan, which has just arrived here from Hollywood, a deeply serious and long fantasy epic – the first in a number of parts, in fact – based on an animated TV series. For a British audience, the film's language is inadvertently flavoured by associations and nuances that are vulgar, abusive, and very, very unfortunate indeed.

The story is set in an imaginary era in which the world is divided into four nations based on the four ancient elements: earth, air, fire and water. The Fire nation is warring with the others for total domination. Yet each nation has a certain type of people, a favoured race different from the rest, people with the Jedi-like power to control or "bend" the elements. Firebenders. Earthbenders. Waterbenders. And airbenders. At the cinema showing I attended, the British crowd reacted derisively at key dialogue moments. One wise old lady says solemnly to a young man: "I could tell at once that you were a bender, and that you would realise your destiny." One character tells another wonderingly: "There are some really powerful benders in the Northern Water Zone." Another whispers tensely: "We want to minimise their bender sources." A key figure is taken away by brutal soldiers, one of whom shouts cruelly: "It's… a bender."

And so on, for almost two hours. Each time, the response from the auditorium was deafeningly immature, and brought many of us to a state of nervous collapse. By the end of the film, I felt like a bit-part player in some feature-length adaptation of Viz comic – Springtime for Finbarr Saunders, perhaps. This scene will inevitably be repeated in every cinema in the land showing The Last Airbender. For Friday and Saturday night showings, the police may have to be called.

But at least this linguistic lurch provided some interest in a film that is mind-bendingly boring, with an utter lack of narrative drive, an absence of jeopardy or anything at all being at stake, or of interest, in any way whatever. After the first five seconds, it seems as if you have been watching it for around two-and-a-half hours, and that this time has passed in four-and-a-half days. And even the glassy-eyed idealism has already been compromised: the film has been widely condemned for recasting the good characters as white, with south Asians only allowed to play the villains. It features the British star Dev Patel, from Slumdog Millionaire, a bright young player who deserves better than this.

It is incredible how awful the once feted director M Night Shyamalan has become and how he is still allowed to make big-budget films. I didn't think it was possible for him to make something worse than his Lady in the Water or The Happening. But he has managed it.