Going to the gym can be an intimidating experience. No matter where you go there is always going to be a gym junkie or two that is absolutely ripped and just looks like a beast. The thing is, this guy has probably been doing this for many many years, probably has a much more dedicated diet than you do, and probably spends a lot more time in the gym than you do.
He is probably also a super nice guy. I have become friends with some of these guys simply by asking them a question about a certain machine and you would be amazed at how willing people are to give out free information.
One things to avoid though, especially if you are new, is trying to emulate the way that these powerhouses work out. They can "Ego Lift" because they have earned it with years of hard work, you on the other hand, are just going to hurt yourself.
This is where you load up the weight stacks with more weight than you can handle and then probably breathe really heavy or even worse grunt or shout to get through some reps. This is my (and everyone else's) most hated person at the gym. No only are you a audible pain in the neck to the rest of the people in the gym, but you are probably not benefiting yourself and you are potentially going to injure yourself and those around you.
I really don't understand why people do it. I'll see a guy doing bicep curls as his first exercise of the day, and because he is surrounded by people that are bigger than he is, he'll reach for the 15s when he should clearly be on the 7.5's or maybe 10's at best. He then struggles to make it through 6 reps while having completely incorrect form and is normally unable to do a second set. Rather than admit that he made a mistake and step it down he'll simply abandon the exercise altogether.
Why do people do this? I am a medium sized dude who works out in a variety of ways and when it comes to most of the things I do in the gym I have a plan and I know exactly what I am doing. I also almost never look at what someone else is doing in the gym unless they are making a spectacle out of it by grunting, screaming, or generally just being a nuisance. So if you are stacking on those plates hoping that I am going to admire you, or anyone else is, you are going to be sorely disappointed since most people don't even pay any attention to others at the gym.
The obvious first reason is because you look like a jackass and you are ruining the overall ambiance of the workout environment with your screaming and antics. Nobody cares bro, it's really as simple as that. Plus if you drop a plate on me because you can't handle the stacks you are trying, I'm gonna throat punch you... ok, not really, but I am gonna get upset and in a real gym they would probably reprimand you or kick you out.
The second, and more selfish reason that you shouldn't do it is because you can and will injure yourself doing this. Form is extremely important in order to avoid injury in lifting, and if you do not have correct form - and you won't if you are lifting far more than you are capable of in a strange attempt to impress other people - you are almost certainly not going to have proper form.
So take it easy gym buddies... you don't need to try to be a superstar during every gym session and it only takes one idiot to ruin everyone's experience with his (or her) screaming and carrying on like a fool.