The homespun superstar was sitting alone on the service from Edinburgh on her way home in Blackburn when the loudmouthed louts began mocking her.
Boyle, 49, at first ignored them but she was eventually left sobbing as the rants got worse.
According to the Scottish press she told her mockers: 'I'm normally patient but I am about to greet, greet, greet. I don't normally get angry with people.' The Britain's Got Talent runner-up continued: 'I'm ashamed of you all - shut up. I'm warning you, it's not funny. You wouldn't like it.'
One eyewitness told The Scottish Sun they were disgusted at how Susan was targeted because of her sensitivity and her fame.
They said: 'Susan was minding her own business on the train. Some people were taking pictures. There were people laughing at her - it was not nice. People noticed she was sobbing - something was upsetting her. She then turned to the people sitting opposite her and told them off. Susan certainly put them in their place - and good for her. It can't be easy dealing with the fame she has but she handled it well."
The incident happened as Boyle took a 30-minute train journey on her way home to Blackburn on Sunday afternoon. A spokeswoman for the 20 million singer refused to comment last night.