The 22-year-old, who told pals he was ?bored? with a fireworks display, copied the stunt from the Jackass movie.
He dropped his trousers, and slipped a powerful Black Cat Thunderbolt between the cheeks of his backside.
A friend set the firework alight and the soldier bent over as the firework exploded in a shower of sparks.
Laughing witnesses at the Sunderland event filmed the episode on a video phone not realising their mate was badly hurt.
The soldier, who had recently returned from a tour of duty in Iraq, ended up in Sunderland Royal Hospital where he is being treated for a scorched colon and other injuries.
John Woodhead, chairman of the Firework Association, said that he had never heard of an incident like it in 45 years.
Mr Woodhead added: ?This sort of thing is beyond belief. We have spent a long time working with the Government to create laws that make fireworks safer and better for the public. This incident is very concerning but hopefully an isolated one.?
_________________________________________________
What an arse! ....and a burnt one at that
