An exclamation used in particularly bad circumstances. Typically followed by the expression "Thanks for nothing," used in a saracastic fashion, even if the speaker has no apparent audience or reason to be displeased with the person to whom he/she is speaking. Commonly used among 5-year-olds with undiagnosed attention deficit disorder or attention deficit hyperactivity disorder, frustrated office workers and people who dislike the word shit because of its pedestrian nature.
John S.: Mrs. Johnson, my mom needs a cup of flour to bake a cake.
Mrs. Johnson: Well, honey, I'm sorry but we just ran out of flour. Please tell your mommy I'm sorry.
John S.: Shithorn! Thanks for nothing!