We know it's your pet peeve, @dancingqueef, but I think people are genuinely interested to know why it bothers you, as reading a book isn't something that has any effect on other people. A book doesn't make a noise, smell or encroach on your space, so what is it about someone reading that annoys you?
Why does someone sitting and having a coffee in silence while reading a book annoy you more than someone sitting and having a coffee in silence while staring out of the window or looking down at the table?
What about reading a newspaper? Would that be just as bad, in your eyes? What about reading a book, but doing it via the Kindle app on a phone? Is that a problem for you or is it paper books only that incur your wrath?
And is it only in coffee shops that you hate seeing people reading a book, or do you also hate seeing people read, say, in the park or on a train? What about the cafes in Waterstone's? Is it OK to read in those cafes because they're part of a bookshop? Or do you think those things shouldn't be combined?
I get that people can't help the way they feel about things and that annoyances aren't always rational, but you must have some idea of why you have a hatred of people reading in a cafe and I'm very genuinely keen to know more.