Asking the FA for help does't always work. On a LAX-DFW flight one evening last year, there was a gentleman in 1A who literally talked non-stop from the time we boarded. It was irritating but I can put up with most infringements so it was not such a big deal to me. However, 2 1/2 hours into the flight, my seat-mate in 2A got so worked up about it, she called the FA/Purser and asked her to say something to the man. She acknowledged that this was the most annoying person she had ever seen on a flight but stated it was out of her jurisdiction to do anything about it.