Apparently you have doubts about the morality of social nudity if you have to ask. Where in God's word does it say that nudity (even social nudity is sinful or immoral as long as there are no sinful thoughts, behavior, lust, or desires involved? Nudity can be sinful or non-sinful--depending on one's thoughts, attitude, actions, and behavior. Does it cause sexual arousal, desires or lust? If so, then it's sinful. Of course, such desires can be experienced while fully dressed; so the lack of clothes doesn't really mean all that much. Personally, I see nothing wrong with nudity as long as there is a complete lack of sinful desires and lust; that is not always possible--depending on the individual. The human body and mind can (and do) learn when nudity is meant to be sexual and when it's not. So, yes, it is possible to be socially nude with other people (even the opposite gender) without sinning.