Why do atheists get mad when people tell them or talk about God ? [Spirituality & Religion]

If you do not believe then that is your business. I will not try to change your own personal beliefs in any way, shape or form. We have people who are believers, and we have people who are not. I am not in the business of patronising anybody for their beliefs or ideology. But if you challenge me, then I will respond as I see fit. That is the difference between trying to teach people, and teaching people when they ask a question.
I often wonder though why some atheists get mad when people tell them or talk about God. Its like they get so offensive, or agitated.
Its like when Democrats and Republicans argue about who is right or wrong.
What do you think SW. ☺