I love it when people straddle the flat bench and proceed to curl the bar or put 10 lbs on each side and curl it. In my gym, the bars of set weight are right next to the flat bench. There's a big pyramid that contains 40-110 lbs of straight bars, but yet, this guy proceeds to do it every time. I've also seen a guy take the bar from the incline bench and hold it straight out while doing crunches. I just want to say "hey jackass, go grab a 45 lb weight and put the fucking bar back"
I always shake my head at dumbass people.
Another one was this girl who just got her personal trainer "certification" and she was bragging about it. I watched her put someone through a workout, and I laughed my ass off to her face. She was spotting this guy on bench. She proceeds to hold the bar then entire time. She's wearing a tight tank top and the black "fuck me" pants you see on college campuses. She bends over right in his face the entire time. I wanted to yell at her.
Later, when I was finished, I was just shooting the shit with her. I was telling her how I can't bench or do any overhead presses because of my shoulder. She says "Oh, there are other things you can do for chest". My response "No, there's only presses and flyes". "No, there are other things you can do, but I can't think of them right now." She then gets this blank stare on her face like she's thinking, and then repeats the last sentence. I wanted to say "I've watched you train people. You're a fucking idiot and you shouldn't be a trainer if you didn't know those are the only types of movements you can do for chest". I know dips work chest to a degree, but I can't do those either, and I told her that.
I hate fucking idiot personal trainers and the people that come in and do half reps. I actually showed a guy how to do front squats the other day. He was really receptive and liked learning things. Of course, I had to disspell some commons myths (going below parallel hurts the knees, etc), but he really appreciated it. Kinda made me feel good.