Atheists, does it irk you that Christians are so sure of their beliefs?

Is part of the problem their absolute certainty that God does exist? Or is really more your feeling that Christians try to force their beliefs on you? Or is it something else entirely?

Christians will say with complete certainty that they will go to heaven when they die and that they will be reunited with their loved ones (those that were saved) who have gone on before them. They are also sure that every other Christian would agree about their certainty that God exists.

So again, in all honesty, does it just irritate the heck out of you that Christians are so sure of their belief in God?