I love showing up gym show offs.
I was doing 180kg leg presses and this guy wanted to work his sets in with me, so I was like "ok cool". He tried my 180kg set up for a few very half arsed reps and he was like "this is too easy". On his next set I told him to go deeper and try a full range of motion, he couldn't even move the weight from its starting position
This is one of those things I always laugh about to myself. There are so many people at the gym who don't actually care about being proper fit or strong, just want to move a lot of weight. So they do half reps, using very little range of motion. One of my personal favorites is the ones who do biceps curls with their arms already bent at the elbows, swinging their entire torso to get the barbell or dumbbells moving, using momentum to lift the weight a few inches instead of their arm muscles.
I guess some people just don't know better, but I see it so often and wonder why they don't just do a quick Google search on good form. It would take literally two minutes.