A long time ago, the original pastor of my church told me "the people who have the most trouble believing the Bible are those who have never read it." Both prior to this discussion, and every day since then, I have found that to be an accurate statement. As much as unbelievers talk a big game, atheists in particular, it's clear that even those who claim to have come out of the Christian faith rarely know much about it. Some of them do not even know the structure of the Bible, and the vast majority of them can only cite Bible verses they have found cited elsewhere. Ironically, I even remember one atheist I debated in the earlier days of my faith who claimed studies show atheists know more about the Bible than Christians, and even sent me a Bible quiz, which was littered with Biblical inaccuracies.
But you don't need my personal anecdotes, you can see it in your own life. Notice how they all know a select few basic laws from the Old Testament; Do not eat pork or shellfish, don't wear mixed fabrics, don't trim the edge of your beard, and occasionally you'll find one who knows that it says don't eat bats (but only because they don't know Biblical taxonomy and want to use their ignorance as an argument). Of the 613 commands in the Old Testament, atheists seem to know less than 10. Which is especially strange, since there's an actual set of 10 called the Decalogue, which they often erroneously believe is how you get to Heaven!
By contrast, there are some other laws far more prominent than the ones typically cited, yet they get completely glossed over by the same atheists who will swear on their left pinkies they've forgotten more about the Bible than you will ever know. As an example, it seems very common that atheists never seem to understand the significance of blood.
There are so many angles from which we can approach the issue of blood, starting with the simple fact that the Bible is actually anomalous in what it preaches about it. The main Mosaic command is "‘And whatever man of the house of Israel, or of the strangers who dwell among you, who eats any blood, I will set My face against that person who eats blood, and will cut him off from among his people. For the life of the flesh is in the blood, and I have given it to you upon the altar to make atonement for your souls; for it is the blood that makes atonement for the soul.’ Therefore I said to the children of Israel, ‘No one among you shall eat blood, nor shall any stranger who dwells among you eat blood.’" (Leviticus 17:10-12).
Of course, there's a lot more the Bible says on the topic, but that's a good starting point. Now, with that in mind, it's quite clear that blood is supposed to stay inside the body. Practices such as bloodletting, therefore, are excluded by divine revelation. Well, in the modern day, we know just how much truth there is in this statement. Not only is blood vitally important for us, but we can now test a person's blood in order to detect a wide variety of health problems early on. In other words, rather than being a bunch of anti-scientific nonsense, as atheists often claim, the Bible is quite scientifically accurate, being ahead of its own time in some cases.
Interestingly, it is also ahead of modern "Christianity". Unable to find solid arguments against Christianity, atheists love to lump it in with other, more easily refuted worldviews. Often, they will do so by simply using "religion" as synonymous with individual religions, rather than a broad category. But actually, because there are various different denominations under the "Christian" umbrella, atheists have living straw men at their disposal.
One of those living straw men is Catholicism, a very prominent pseudo-Christian religion that atheists love to attack. Now, ironically, most of their arguments against Catholicism don't work especially well either. The Crusades, for example, are hardly testament to the fact that Catholicism is not true, much less Christianity. However, because of the Catholic doctrine of the Eucharist, in which the bread and wine of the Lord's Supper is believed to literally become the flesh and blood of Jesus, the fact that the Bible literally forbids the consumption of blood means not only is it easy to prove Catholicism is a false version of Christianity, but even the supposed first Pope would have utterly rejected it on this fact alone.
A third angle from which to approach the Biblical attitude to blood is lost on the vast majority of atheists, even the smarter ones. See, although the specific categories are not mentioned by name in the Bible, there are different categories of command. Most notably, the Old Testament law is commonly divided into three categories: Moral law, civil/judicial law, and ceremonial law. Of these three categories, only one is designed to be obeyed by all people at all times, that of course being moral law. The rest were not actually intended to be obeyed by modern Christians. This is why we do not need to be circumcised, why we are free to eat the meat of "unclean" animals like pigs, why we can get tattoos etc.
And if you know anything about the Bible at all, you should know this stuff, because it is the entire point of those laws existing in the first place! The New Testament repeatedly points back to the Old, telling us, first of all, that it is old. Hebrews 8:13, for example, points back to Jeremiah 31:31, in which God promises a new covenant. He then says that "...what is old and aging is about to disappear...".
But of course, you can't just get rid of your foundation. The Old Testament still has to stay in the Bible, or the New Testament makes no sense. But it is applied differently. Paul says it best in Galatians 2:22-25: "But the Scripture has confined all under sin, that the promise by faith in Jesus Christ might be given to those who believe. But before faith came, we were kept under guard by the law, kept for the faith which would afterward be revealed. Therefore the law was our tutor to bring us to Christ, that we might be justified by faith. But after faith has come, we are no longer under a tutor."
You see, then, that the Old Testament isn't just some long list of "thou shalt nots", as atheists often treat it. Rather, there are highly advanced reasons behind every single one of them. Without them, we wouldn't know why Jesus came, or even who He is.
You see, then, that if you run around a church pointing at every bacon sandwich and saying "your Bible says not to eat that", you are demonstrating the highest degree of ignorance. You've missed the point! You've proven you don't know the vital context behind the verses you cite! It's not about your shaving habits, the material of your clothes, the food on your plate etc. It's about God, and how we relate to Him.
Specifically, we are sinners. From the very first sin in the Garden of Eden, right to the last evil thought in your head, mankind has been in rebellion to God. And the wages of sin is death. But through a long and complex history, God both foretold and delivered a Savior, Jesus, His Son, who was born of a virgin, lived a life free of sin, and died on the cross. Through this sacrifice, Jesus redeemed the lives of all who believe in Him.