I have the opportunity to work out in many different gyms in the United States and a few in Mexico and a dynamic I see more often than not is what I call "hero lifting." It involves using heavy weight (much heavier than one can really handle) and handling it by lifting it (or more often than not) not lifting it properly.
A couple of examples:
Leg Press - The way this works your legs effectively is to put your feet low on the pad and bring your knees to your chest -- a full, long movement. The "hero" move is to load a couple of extra plates on, put the feet high on the pad and drop it about 4 or 5 inches. Or, even worse, drop it a few inches and then put the hands on the knees and help press it back up. That's worthless to build leg strength but a great ego booster. The same is true with squats and hack squats. They are a cheater's paradise because the movement can be truncated easily so as to completely avoid working the quadriceps.
Bench Press - Same song, second verse. A bench press involves bringing the weight to the chest, touching it lightly and then pushing it back to full extension. The "hero" move is to load up the bar and drop it about 4 or 5 inches (sometimes even less than that) and then get up and make sure everyone in the gym has seen just how much weight you can (but really can't) handle.
Bottom line? Decide what you want to work -- your muscles or your ego. If the former, leave the latter outside the gym and just come in, work hard and do what you can do properly and effectively.
Train hard; diet harder.