The guy that wears a weight belt the whole workout. By wearing this belt during the whole workout you are teaching your core that it doesn’t have to do its job. Your core is there to provide stability (see "The Core: Your Body's Transmission"). If you use the belt you are telling your core that the belt will do the work and you don’t have to. There are times wearing a weight belt may be necessary. Usually it is during heavy squats or deadlifts. Wearing a weight belt while doing bicep curls does nothing for you. We are in the gym to become stronger not weaker, stop it!
The no warm up person. This person goes directly to the bench press and knocks out 3 sets with 225 lbs. Great job! By not warming up you are opening yourself up to injury. Your rotator cuff and other stabilizing muscles of the shoulder girdle need to have a proper warm up to allow for the most stability during an exercise like the bench press. A lot of times a proper warm up can even give you greater strength while doing exercises like the bench press.
The trainer that gives their client a workout, but doesn’t correct movements, allowing incorrect movement patterns to be ingrained into the brain of their client perpetuating injury prone movements. Sorry to bash on any of my fellow trainers, but this upsets me tremendously. We are responsible for our clients and their well-being. A great example I once witnessed, a fellow trainer had a client who cannot properly stabilize their shoulder doing Cable Tricep Extensions. The client rounded their shoulders forward and yanked down on the cable using their entire body. I didn’t know that a Cable Tricep Extension was a full body exercise. Nor did I know that to do the exercise you had to use your superior traps. If this is you, learn and grow, become a better trainer.
Range of motion or lack thereof it. I observe people doing a lot of different exercises without using full range of motion. I know we can all be guilty of this at times, but we should all strive to go through full range of motion. A lot of times it is vanity that causes us to fore go range of motion in favor of heavier weights. Which I understand, I want to lift heavy all the time but sometimes you are only causing instability and increasing risk of injury. We all see the bicep curl guy that every time they do bicep curls they stop about 3/4s of the way down and start to curl back up. What happened to the bottom portion of the bicep curl? I know it is harder, but that is your limiting factor. Go down in weight and do it right.
This is just a pet peeve of mine. Put your weights away!!! You are not the only one who likes to use the leg press!! If you cannot lift the 100lb dumbbells to put them away you shouldn’t lift them to do Dumbbell Bench Press either! Gym etiquette people!!!