The Scottish singing sensation - who shot to worldwide fame following her performances on UK TV show `Britain`s Got Talent` last year - broke down in tears before blasting the teenagers who had taunted her.
Susan - who mouthed "f**k off" at someone who took her photograph - reportedly defended herself saying: "I`m ashamed of you all. Shut up. I don`t normally get angry. It`s not funny. If it was you, you wouldn`t like it."
The `Wild Horses` singer was alone on the 30-minute journey from Edinburgh, Scotland to her home town of Blackburn, West Lothian on Sunday (22.08.10).
An onlooker who witnessed the row praised the way 49-year-old Susan had conducted herself.
The source told The Sun newspaper: "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."
Although the singer is worth an estimated £10 million, her brother Gerry claims she is living on just £300 a week and has to use public transport.
He said recently: "Susan said to me, `I`ve been told I get £300 a week because I`m a novice.`
"She should be riding high, developing her career, travelling the world. She shouldn`t be worried about money when she has millions in the bank."