gratuitous
adj.adj. done without any good reason or purpose. You use this to describe something that is unnecessary or just added to make a situation more shocking or exciting.
adj. done without necessity, justification, or reason; excessive or superfluous. Often carries a negative connotation of being unnecessary or intended to provoke.
The movie includes some gratuitous violence that serves no plot purpose.
The politician's comments were seen as gratuitous, as they were designed to offend his opponents rather than inform the public.
The author's use of gratuitous descriptions of the setting often distracts the reader from the subtle character development that defines the novel's emotional core.
From Latin grātuītus (“free”), from Latin grātia (“favor”), grātus (“showing favor”).