I sleep naked (sorry I'm so blunt) and when I go camping or have a friend stay the night, I tell them I sleep in the nude and they are ok with it. Sometimes they sleep in the nude. I don't mind and I don't look at others with lust, but I get an erection sometimes. Is this normal and or a sin to just hang out with no clothes on, and to get an erection even thought I have no feeling for him that way? Am I gay?
You've raised several issues, so let's work through them one at a time.
Let's start out with your body's reaction. Erections are caused by a small muscle inside your pelvic region at the base of your penis. It clamps down on the vein that brings the blood away from your genitals and back toward your heart. Because blood enters the penis faster than it can leave, your penis swells up like a balloon, and just like a balloon, it gets stiff and hard.
When you first develop the ability to have an erection (about two years after reaching puberty), your brain doesn't know what to do with the new ability. Concepts, such as erections and sexual feelings, are brand new and so your brain experiments. I'm sure you remember several years ago that your penis became erect at all sorts of times for no particular reason. This was your brain experimenting. Your reaction gave your brain feedback to say, "Oops! Wrong time." As you get older these incidences are less frequent, but they don't go away totally. It is just something all men have to learn to put up with.
You didn't mention when you are having the erections, but you should be having four to five erections each night as you sleep. This is a part of how the male body works. There is a phase of sleeping called REM (Rapid Eye Movement) in which all men have erections. It is also the phase of sleep when you dream. Sleep goes in cycles and you usually go through the REM phase four or five times each night.
One of the big mistakes young men make is assuming that their body's physical response is an indication of their thoughts. Yes, if you think about sexual situations, your body will respond, but the other way around is not necessarily true. You might have gotten an erection when you stood up in front of the class to give a book report. That certainly had nothing to do with sex or sexual thoughts; your body was responding to your tension from being nervous. Similarly, you might get erections while you are in the shower. No one else is around and you aren't thinking about sex, but your body is simply responding to touch as it is supposed to do. Just because your penis gets erect in front of other men it does not mean you're gay.
How you like to sleep is your choice, but you are old enough that you can't just consider what you like to do at all times. You have to consider the impact your choices make on other people. The general rule since the fall of man is that a person doesn't expose their genitals to others. We make efforts to keep our privates private. Of course there will always be times when it can't be avoided, yet we should make efforts to minimize it. Being seen naked in front of others ought to trigger a sense of shame. "Your nakedness shall be uncovered, Yes, your shame will be seen" (Isaiah 47:3).
Let me use the example of Ham (Genesis 9:20-27). Ham's father, Noah, sinned by making wine and getting drunk. Ham accidentally walked in on Noah while he laid naked in his tent. Rather than be embarrassed by the situation, Ham went to his brothers. We aren't told what he said, but it is likely he thought it was funny that their father was acting so poorly. I want you to particularly note Japheth and Shem's response. "But Shem and Japheth took a garment, laid it on both their shoulders, and went backward and covered the nakedness of their father. Their faces were turned away, and they did not see their father's nakedness" (Genesis 9:23). I'm sure that over the years there were many occassions when they might have seen their father without clothes. They could have just walked in and covered him up, but they were making a strong point. Their father, because of his drunkenness, was in an embarrassing state and they refused to see their father lowered in their eyes. Thus they went out of their way to make sure they didn't see Noah uncovered.
While you don't find the idea of being naked in front of other men bothersome, you don't know the thoughts of others. Some might not care, but others might find it difficult to control their thoughts. Some might go along with what you do, not because they normally do the same, but because they don't want to be different. Paul talks about people compromising their personal sensibility and doing things they are not certain is right. In this case it is talking about eating meat that might have been sacrificed to an idol, but the principle is something we should be aware of: "Do not destroy the work of God for the sake of food. All things indeed are pure, but it is evil for the man who eats with offense. It is good neither to eat meat nor drink wine nor do anything by which your brother stumbles or is offended or is made weak. Do you have faith? Have it to yourself before God. Happy is he who does not condemn himself in what he approves. But he who doubts is condemned if he eats, because he does not eat from faith; for whatever is not from faith is sin" (Romans 14:20-23).
So what should you do? Be consciencious of others and their sensibilities. If you're camping and you want to sleep nude, keep covered until after you crawl into your sleeping bag and then you can take your clothes off (and by the way, if it is cold, keeping some clothes in your bag lets you get dressed with something warm in the morning). If someone is sleeping over, wait until you get under the sheets to take the last of your clothes off. There is no need to announce what you are doing to others. If someone else is naked, simply avert your eyes out of respect for them.
Rather than numbing yourself by repeated exposure to the sense of shame that is built into all adults, give credence to it. One of the complaints God had against ancient Israel was the fact that they lost their sense of shame. ""Were they ashamed when they had committed abomination? No! They were not at all ashamed; nor did they know how to blush. Therefore they shall fall among those who fall; at the time I punish them, they shall be cast down," says the LORD" (Jeremiah 6:15; see also Jeremiah 8:12). Therefore, whether being nude bothers you or not, act as one trying to keep a sense of what may be embarrassing to others.