A straw man argument is when an opponent of a belief misrepresents that belief, and then proceeds to attack that misrepresentation, giving the appearance that he has refuted the original belief when really, it has been left unscathed. No one liner has ever exemplified atheistic straw man arguments more than "I prayed for a bike, but then I realised God doesn't work like that, so I stole a bike and asked for forgiveness instead."
Prayer is one thing no atheist seems to be able to get their head around. Most atheists believe prayer is a master-servant relationship. And they're actually right, but in the opposite direction. No Christian should ever presume that prayer is a means of controlling God. Rather, in any situation, God is always the Master. He can say yes to a prayer, He can say no to a prayer, He can answer some bits of a prayer, He can reject other bits of a prayer, and if He so desires, He can even completely ignore the fact that a prayer ever happened.
There are two critical things the Bible says about prayer. The first is that a Christian prays according to the will of God (1 John 5:14). As I said, God is the Master in this relationship. If God, in His infinite wisdom, decides not to answer a prayer, that's entirely His prerogative. Even Jesus, leading up to His crucifixion, asked that the Lord would provide another way, so that He might not be crucified, and yet famously, He declared "not as I will, but as you will" (Matthew 26:39). Jesus, of course, was still crucified, proving that even God's own Son does not always get the response He desires.
The second thing, specifically relating to the bike, is that our motive counts. James 4:3 tells us that if we ask amiss, we do not receive. If you ask for something with the wrong motives, you have a significantly lower chance of getting the desired response. This is especially relevant to every atheistic test prayer ever. The majority of atheists pray specifically with the intention of proving God does not exist. So, why would He answer?
But whoever wrote this one liner apparently knows at least some of this. "I know God doesn't work like that..." suggests he knew God doesn't work like that, presumably as a result of asking a Christian why God doesn't work like that. But apparently, they do think God works in another way He absolutely doesn't. Can a Christian really just steal a bike, ask for forgiveness, and be done with that? Certainly not! How shall we who died to sin live any longer in it? If you think I'm just making this up as a response to the joke, look no further than Romans 6:1-2, a verse in which Paul refutes this very mentality with those very words!
A Christian can't just sin and pray for forgiveness as if that's all well and good. The whole point of Christianity is that sin is bad, sin deserves punishment, and Jesus took that punishment on our behalf. Now, if you believe sin is worthy of punishment, why would you just do it anyway?
To put an earthly spin on this, let us take the friendship I share with my friend "Layla". Together, we have been through a lot. We've sinned against each other, but our love is powerful enough that all we need is to ask forgiveness, and we drop the matter entirely. We don't even keep a list of all the wrong things we do against each other; our wrongs are forgiven even before we do them. Does this excuse those wrongs? If I know that Layla is willing to forget every idle word, does that give me the right to say something cruel? If Layla knows that I am willing to forget every idle word she says to me, does that give her the right to be spiteful? Of course not! Our will to forgive each other does not make the things we forgive each other for any less evil. The whole point of forgiveness is that the person receiving forgiveness has done something that requires forgiveness.
In the same way, the fact that Jesus has taken our punishment for sin upon Himself does not make sin any less detestable. If anything, it makes it worse. If I truly love Jesus, how can I possibly say it's totally cool to just sin and ask for forgiveness?
The point of the cross is to free believers from sin in two ways. The first is to free us from the eternal consequences of sin (Hell), but the second is to free us from sin itself. Whereas unbelievers are so captivated by their sin that they can actually convince themselves that their sin is no sin at all, Christians are free to disobey the devil himself and submit themselves faithfully to God. This means that although Jesus can absolutely forgive us for stealing a bike, it is our right and responsibility to not steal that bike, and if we are truly Christians, we won't even want to.
Unfortunately, during this life, no Christian will ever be perfect. The Bible even goes as far as to say that if we say we have no sin, we are deceiving ourselves and the truth is not in us (1 John 1:8). Nevertheless, sin is always to be regarded as an enemy to shun, not as a friend you're kind of free to hang out with but your dad isn't entirely pleased about it. Sin is a filthy harlot trying to convince you to cheat on your spouse. A siren leading you to crash your boat into the rocks. Sin is what Jesus died for.
And He did that for you, too. If you're not a Christian today, you're still a slave to sin. But nothing says you have to be. Come to Jesus in faith, and He can give you the same freedom He has granted to millions of people over the last 2,000 years. It's a gift just waiting for you to take. And trust me, that's better than any bike you could ever pray for.