Brainstorm

[Aegon]

1. "A person who is utterly intolerant of differing creed, belief, or opinion."

That definition is slightly ambiguous. Are we talking about any differing creed, belief or opinion from your own and what do we mean by utterly intolerant?

2. Oh, the irony! You being an atheist should mean only one thing about you (that you do not believe in God.) Being a Muslim, however, should also only mean a few things about you (that you believe in God and you consider the Quoran your holy book.) If you assume anything about their beliefs past that (including how much of the Quoran they know of and how literally they interpret it) then it's no different than me assuming you're an intolerant cockface because you're an atheist.  

It's not about what it should or it shouldn't. It's merely what it is. Being an atheist does mean simply not believing in God. That could make other persons suspicious(if he doesn't believe in God, does that mean he is exactly the opposite of what the bible describes as good?). The only difference being, when you're talking about a muslim, as you yourself pointed out, you're saying they believe in a certain thing and that they follow a certain book. There is no same thing when you're talking about an atheist. There is no book and no belief to be had. In fact it's the rejection of those things that makes one an atheist, to a certain extent.

It's not my problem that muslims choose to adhere to those ideas and it's not for me to think about how much of a muslim are they when I think about making friends or having a beer with someone. If they don't want me to jump to justified conclusions they shouldn't publicly identify as muslims.

(Bolded by me)

If you don't see the problem with you saying that then I'm not sure how to respond.