If there is any narrative device that I hate, it's stream of consciousness.
Stream of consciousness refers to a style of narrative voice (how you tell the story) that emulates the actual way someone thinks. These works are told from the first person perspective (the "I" point of of view) and jump from idea to idea without pause. The style generally lacks standard punctuation and is filled with allusions (references to other works) and long periods of non-plot tangents.
While the style appeared before the Modernist period, it was the Modernists James Joyce and Virginia Woolf who capitalized and defined the narrative device. They are considered its masters, along with some of their other contemporaries. (The Modern period of literature refers not to modern times, but rather to the literature that developed between in the first half of the 20th century.)
The idea behind stream of consciousness, the one that the Modernists grabbed onto, was to truly get inside someone else's head. The idea of the novel at the time was as a constructed fiction - something with rules and boundaries. The Modernists wanted to get rid of that idea. Their goal was to remove the artifice inherent in structured sentences and plots, and to simply express a recreation of the human mind, and thus the human experience, as it is. The closer you could get to the actual way a person thought, the better the work was.
I hate it because I find it more artificial than structured work. (Just my opinion.)