Since I didn't grow up with casual nudity and was taught one's body parts were private and should only be presented for the purpose of sex with the opposite gender, my first experience with showering in Basic Training was somewhat uncomfortable and I tried not to draw attention to myself while nude as much as possible. But after a fashion and repeated exposure it become less so as I realized that being self-consciousness was somewhat silly since there wasn't anything sexual about it to me and I'm pretty sure, to most of the other guys.
As far as open displays of sex such as group wanking, no offense, but this is nothing more than a mere fantasy of gay or bi men wishing what the military is, but it is not. This is not to say it didn't or doesn't ever happen, but one must realize based upon national percentages that most of the dudes that enlist are straight thus have no interest in other men. Add to the fact that back when I was in during Desert Storm in the early 90's, the military was very adamant about weeding out anything perceived as homosexual as this was before even "Don't ask, don't tell"; let alone all the progressive changes since then. So, if things like circle jerks did happen, I had no knowledge, nor did anyone else I knew as announcing it to the wrong person would be risking a dishonorable discharge.