And, don't touch them at all. They will defend themselves if you hit them, and you'll probably end up in the hospital. Instructors are a different breed, and they expect problems and are not afraid of confrontation.
Yes, they do. They don't do it to insult you or intimidate you, they do it to break you. They have to weed out those who can't withstand the pressure. It's just a game they play with your mind--a head game. Besides, you will also be given a psych test to make sure you're not a whack job. But, if you do what you are told as instructed, you will have less problems adjusting. Remember, too, it's just while you're at boot camp.
When I was about to leave Air Force basic training, I got assigned to guard the dorms of newly assigned airmen. While sitting in the office watching over the entire dorms while the sergeant who was actually in charge slept, a call over the intercom came in that some guy was freaking out. I told the other guy sitting with me to wake up the sergeant, while I go see what's going on. When I got up there, this young guy was screaming and crying that he wanted to go home, and was trying to choke himself with his own dog tags, which you can't really do, but man was he crying like a baby.
He and his squad had just arrived that morning, and he just couldn't take the pressure and the instructors yelling at him. I calmed him down, knowing the sergeant would be there very quickly, and the yelling was going to get worse. He stopped crying, but was whimpering. I told him it's just a head game--the instructors want to break you. Don't let them. They can't physically touch you like in the movies, so it's just a lot of screaming in your face. You're being tested mentally. Can you hold up? And, it's only for a short time, after that, you're gonna be busy training in a classroom, marching, and doing things in the field. And, yes, when the sergeant got there, he screamed a lot and ridiculed the young guy for being a baby. "Why are you crying? You don't see anyone else crying, do you? They woke me up for this sh*t--a f*cking crybaby! You wanna go home, so you can cry to your mommy? Unf*ckingbelievable!"
My grandfather used to be an Air Force basic training instructor during the early years of the Air Force. He would get a friend of his to pose as a trainee, and during the first few days of basic training, when everyone was in formation, his friend would purposely do something wrong, and my grandfather would grab him and hit him with fake punches to the gut, throw him down, and kick him a few times, which would scare the crap out of the other trainees. Tricks of the trade that work. After a few days, the friend would drop out due to the pressure from basic training. He would do this with all his new squads. Today, instructors can't beat you, but they can yell at you like crazy. Just ignore the spit when it hits you in the face.
Years ago, professional boxer Riddick Bowe, after semi-retiring from boxing, decided to join the Marines to make his mother proud and rededicate himself to training. He laughed when instructors yelled at him, and he lasted just three days in the corps. He thought it was a joke that some smaller guy was yelling at him. He was never gonna be a marine and didn't take it seriously.
Instructors are doing a job, and if you should complete boot camp, they've done their jobs well, and you'll remember them not for yelling at you, but how they instilled discipline, taught you so many things to get you acclimated into the military, and how, believe or not, took responsibility for you for the entire time you were in boot camp. Try taking responsibility for 30 people, some who have never been yelled at in their lives, or never been away from mommy for more than one night. I started playing sports at a very young age, so I've been yelled at and grabbed by the shoulders a lot. Basic training was just a head game to me, and I never took it personally.