Have you noticed how when you're travelling alone on a plane you always get a seat next to someone who wants to talk when you want to read? And they want to talk about the most boring subject on earth, or even at a couple of thousand feet; often enough it is either about themselves or about American football. And they will be impervious to the usual discouraging body-language and polite brush-offs like `I'm sorry, but I want to read' or `I need to finish this before we arrive.'
Last time this happened to me, it took almost half the flight to escalate to the `Will you shut up, I want to read' stage that eventually worked.
This year I have resolved that in future I will eschew `I'm sorry...' and all that refined subtlety; next time the opening gambit will probably be `I'm obnoxious and you can shut up.'