I've encountered some interesting and often very silly objections as to why someone would be an atheist or what the motivates someone to be an atheist. Atheism is the lack of a belief in a god or gods. The lack of the belief is NOT a belief in and of itself. Think of it like this; If you are walking through a market and someone attempts to sell you something and you say "no, thank you" or something of that sort. Is your not buying what someone is trying to sell you a different kind of "buying"? Of course not. You are simply rejecting what's being presented to you and atheism works in the same way. When someone says that their god or gods exist we demand evidence for their claims. Until evidence, not arguments, are presented an atheist will not believe the claims(about the existence of gods). Here are some objections and answers.
1. You cannot prove that my god does not exist.
Answer: It's not my job to prove that your god exists. You are asserting that your god exists. You are making a positive claim and just like a court of law, if you make the claim, you must provide evidence to support that claim. You do not get to pass your job off to me and then declare that I am incompetent.
2. You're an atheist because you just want to sin.
Answer: That claim has a few unstated foundational premises. The first is that the atheist accepts the concept of sin as valid and that "sin" actually exists at all. The motivation for being an atheist is called into question as well in a sort of X Y formation(You are X because you want to do Y). The objection is baloney. I accept the concept of sin as valid only when I want to mess around with religious types. Sin is a religious hangup, not an atheist hangup.
3. You're an atheist because you have had a bad experience in church or with god.
Answer: The claim already has built into it that god exists. How else would I have a bad experience if that part is not granted? The theist already thinks that part is proven ergo the back end of the objection. The church part is interesting. I have had both good and bad experiences in churches but I've also had good and bad experiences in all other buildings. The experience alone is not the reason I lack the belief in the god within the objection. It's the lack of evidence that supports the existence of the god in question. The "bad experience" is trying to highlight that you are only an atheist in virtue of that experience and without it, you wouldn't be an atheist. There are plenty of atheists that have had good experiences in churches and they still do not believe. If I met an atheist who expressed to me they are only an atheist because of bad experiences, I would challenge her or him to go back and think about their reasoning. I doubt that many atheists are atheists because of bad experiences though.
Addition: Bad Experience could be something like being forced to pray, shamed in front of peers for not knowing particular scriptures at a young age, being ridiculed for having an abortion etc.
4. You're an atheist because you hate god.
Answer: Which god? Seriously though, this objection maintains that the god in question has been proven to exist and does exist AND that the atheist hates it. Scroll back up to see what an atheist is for a reminder. How can an atheist hate that which she/he lacks belief? It's like claiming that I hate flying pink monkeys with teapots circling their tales. There is a group of people that hate god and they are called MISOTHEISTS. Atheists by definition CANNOT hate something that is unproven.
5. Atheism lacks morals.
Answer: Atheism is only an expressed doubt about theistic claims(this is just another way of saying what I have stated in the opening paragraph). Nothing more, nothing less. I call this move "dismissal by unnecessary attachment". Those who use this tactic, unnecessarily attach an attribute which they think is necessary to atheism, simply to say "look, it's not there so the entire position is untenable". BULL SHIT. That's like dismissing evolution because it does not also tell me about planet formation or tossing out my refrigerator because it does not also mow my lawn. Atheism does not NEED a moral system to be a tenable position and it is not lacking or insufficient because it does not have one. The theist gets her/his morals from one book or place and the expectation is that the atheist must do the same. Not true by a long shot.
6. You must know everything and think you are some kind of genius.
Answer: In fact I do think I am a genius but that is totally irrelevant to proving your claims and it's untrue that I think I know everything. I am very ignorant of many things and subjects on this planet. The various believers make claims of knowing everything or the origins of things and I do not. Saying "I don't know" is a much better/honest reply when I don't know, as opposed to not knowing and making up some vague explanation to claim I do know what I don't.
7. On your death bed you will believe in god.
Answer: I won't. This objection is of the dogmatic/fear mongering form. Yes we will all die and the theist thinks the atheist will cave before her/his last breath. That's some fanciful wishful thinking and I have no plans to "confess" when my life is about to end.
8. Many people believe in god and there are only a few atheists. You guys are wrong.
Answer: It's okay to think we are wrong but just because you have more people than we do, does not automatically make your claims or beliefs true. Billions of people can be mistaken in/about their beliefs. Billions of people can lack sufficient evidence to support their beliefs. The bandwagon appeal does not get you off of the hook. If more people still believed that Elvis or Michael Jackson were still alive as opposed to those that do not, are Elvis and Michael Jackson still alive?
9. God is calling you but you have chosen to turn your back on him.
Answer: This objection too is claiming that the god in question has been proven to exist and exists and the atheist is "turning her/his back on god". For starters, what kind of phone service would I need for the call to take place?(Better not be Sprint or T-Mobile or the call will be dropped). This one wreaks of some earlier objections and has the idea of free-will tacitly attached. You have to first prove that your god exists in order for it to call me(god can dial? What kind of phone does it have? According to some theists, Steve Jobs has one specifically for god. Call it the iGod1 or something) or for me to turn my back on it. If you want to claim that the call is in some metaphorical sense, then that just appears like a convenient apologetic answer to which you have no basis. It's an assertion alone and assertions alone without evidence are just assertions.
10. God loves you whether you believe in him or not.
Answer: This is just another baseless assertion. You stating it does not make the specific contents of the statement nor the entire statement true in any sense. This is a play on the idea of love and is used as an emotive answer to obfuscate the fact that the linguistic statement lacks any evidence or proof of what it claims.
It's also a "you cannot escape" line.
This list is not the most comprehensive you will find and as I see more objections I will add them or you can add them in the comments section.