Indeed, one way to disrupt this is to think of the people we are comfortable with, what we have in common and what we talk about. These last two might not always coincide either: some things we have in common might be always left unsaid - they seem obvious and/or unimportant, whereas some we might spend lots of time talking about and exploring our commonality, because we see them as important. Importantly, these change depending on who we are with, where we are and what we are doing: it's all about how we navigate our sociality. And this can lead to situations where people see the same situation in very different lights.
A few months ago I was interviewing a young woman as part of my work, and we were talking about Islamophobia. And what stuck in my head was her saying that she thought it Islamophobic if people didn't ask her about her religion (she was visibly Muslim, wearing the veil). I hadn't asked her about her religion. Afterwards I thought about the absurdity of this position, from my perspective. I'm atheist, and I don't really care about someone's personal religiosity although I do take an interest in the relationship between religion and society. That's not to say that I would shy away from talking about religious views, but I don't think it's something I need to ask people about in normal conversation. This is why I don't ask religious friends about their practice or beliefs: I currently spend time with a few Christian ministers, but I don't talk to them about religion. If I asked the young woman about her religion, I'd be being Islamophobic.
At the same time, the young woman could either a) enjoy talking about religious beliefs with religious friends (whether Muslims or other), and/or b) think that religious identity is important (and everyone agrees), so that on meeting someone of a different religion, this would be a natural conversation. Thus, religion would be something that one would automatically talk about, but only in certain contexts. However, thinking about what I want to talk about is very different. Like many people with a middle-class job (and not only them, for sure), I partially define myself by my job... that's why 'what do you do?' is a common question. With friends I often talk about work - more than friends who are in what are euphemistically called 'routine occupations'. On a more random note, I think I must define myself a bit by my transport choices: I cycle a fair bit, and so end up chatting to other commuters about taking bikes on trains, asking how they find it, what their ride is like and so on.
And then there is the problem of British social awkwardness... We don't like it if we don't know whether we'll have something to talk about when we meet someone new, and are wary of offending people. There's a great piece by Bernard Guerin about racial discrimination without assuming racism or racists (http://journals.uic.edu/ojs/index.php/bsi/article/view/120/152), which demonstrates how not knowing what to do or say, in a situation where 'race' is assumed to make a difference, can result in unintentional racial discrimination. We shouldn't assume that someone is racist, or Islamophobic, or anything else, based on them not being sure of exactly how they should act when encountering difference.
Indeed, it would be all so much easier if the ethno-religious identity was the only important thing for everyone. We'd all have our box - there'd be a finite number - and we'd know how we should act. But people are so much more interesting... I'm not Islamophobic because I want to talk about work or music to the woman in a veil, and she isn't a religious obsessive because she's interested in my take on religion. And given an hour or so of a wide-ranging natter, we'd be able to work this out. Assuming that a particular divide is going to make things awkward is a sure-fire way to make sure it does.