[Faceman]

this is the thin line between agnosticism and atheism
harshly simplified
agnosticism:
"I don't know if there's a god , how can I believe in something I don't know exists. You belief in god, go ahead. You defy god, be my guest. I'm not taking sides, I absolutely have no clue who's right."
.
atheism: "There is no god! I know that there is no god. You believe in god, you're wrong. You sya you don't know, what a sissy."
.
I admit this is really dumbed down, but my point is that atheism is nothing but reversed faith and that makes it possible for atheists to cross the line in the same way strong believers may sometimes do (yes, I would be offended by Yorick's example line). An atheist is in fact a believer, he "believes that not" (the agnosticist simply "doesnt believe").
Or as the philosopher would put it: By negating god atheists acknowledge his existence, because you cannot negate something that does not exist.
The bottom line is: Believe what you want to, may you be a Catholic, Baptist, Muslim, Jew, Atheist, Agnosticist (well, then you actually don't believe), Buddhist, Taoist, Hindu, Shintoist,...
BUT don't rub it in to other people
faith (or non-faith) is a private matter and it's rude to attack it.
It's like constantly bragging how your car is better/the other car is trash, only worse.