I have seen a couple but here are a couple that are especially bad/funny.
1. Full body bicep curls - weight is too heavy so they heave with entire body.
2. Full body rows - weight is too heavy so they heave with entire body.
3. Half squats - weight is too heavy so they do a partial goodmorning/squat.
4. Barbell back squat jumps - they half squat, then jump, lol.
5. Static hold leg press - weight is too heavy so they lock their knees to hold the weight in the air for several seconds.
A guy at the last university gym I went to was severely guilty of #1. He was a super nice guy, but he just had a consistently bad habit of using way too much weight. He'd grab the 90 or 100# dumbbells and would, as mentioned above, swing his entire body to get the things. He'd then repeat this process for a good 3 or 4 reps.
He also did the equivalent of this on benchpress. I remember having to spot him one time--I had to basically deadlift the bar off of his chest after the first rep. He then wanted to do five more reps. No clue what he thought he was getting out of it.