You may argue with my definitions, but that's fine. There are almost as many definitions of flash fiction as there are writers of flash fiction.
At any rate, Flash Fiction is NOT...
...a story summary. If your flash story has nothing but blocks of narrative, it's probably a story summary, rather than a fully fleshed-out story with active scenes and dialogue.
...a dialogue fest--or the opposite of a story summary. If your story is nothing but dialogue you're probably leaving out all the stuff that really makes your story interesting and penetrating in order to try to get the basics of the story in by leaving out the narrative and just stuffing in all the dialogue.
...a chapter from a novel. A novel chapter almost never stands alone as a story. Novels are structured so that crucial information is doled out a little at a time, as it becomes relevant to the story. By snatching a chapter out of the novel and calling it flash fiction, the writer offers a confusing mess with no complete conflict/resolution cycle.
...a venue for your teen/frustrated male/homosexual sexual fantasy. There are places for that sort of writing. Most reputable markets are NOT those sorts of places.
With the exception of the last, all these NOTs have exceptions. I've read them. I've read novel chapters that could stand alone perfectly well, and stories that were nothing but dialogue that worked beautifully, and stories that were nothing but narrative that also worked well.
But what all those exceptions DID have were a clean, clear conflict/resolution cycle, a story uncluttered by extraneous information and characters, a story that effectively created characters that were both believable and likeable.
None of that is easy to do. It takes work, study, and practice.