It's a saying in which you say out of sheer fustration instead of actually swearing.
What you tell people what it means may vary but commonly used as That's not nice.
However what your really saying is Fuck You And The Horse You Rode On.
In a professional setting or a place with parents and their children. Instead of embarassing yourself by cussing like an idiot. Simply in a calmly matter say Fuathryo. To them, It may be another language.
After being told by my best friend that he cheated with my girlfriend; Realizing my daughter was in the room, I told him fuathryo and left.