John Malone, 39, was pulled half-naked from the wreckage in Chiang Rai, Thailand, on Wednesday morning.
A naked Thai woman was also found in the backseat with him.
The Irishman had been one of three passengers in a speeding black Sazuki Swift when it hit a concrete post after losing control at around 1am.
CCTV footage showed the brutal collision, which caused the car to flip several times.
A spokesman for volunteer rescue foundation Siam Ruam said: ‘One foreign man died in the crash. The staff helped to bring out the bodies and give first aid.
‘This was a black Suziki Swift and it was speeding.
‘We think the man was having sex or maybe a blowjob in the the car.
‘There were three Thai people and one foreign man. Two of them were women. They were injured and the driver was unconscious but only the man died.’
Pictures showed Mr Malone lying naked on a stretcher after a small blue t-shirt he had on was removed.
The Thai male driver and the female front seat passenger were rushed to Kasemrad Sriburin General Hospital and are currently in a serious condition.
Mr Malone was an English teacher and had worked for a number of years at The Learning Center, in Chiang Rai.
The company paid tribute to him online, saying: ‘We have lost today one of our beloved teachers, John Malone.