Dude, I've seen it all over the years at the facility I work at. All sorts of douchebaggery and a lot of WTF is going on here type of shit with people's exercises. One of the best is people using the standing calf press machine as a squat/legpress workout.
Tonight was good tho, had a guy who thought someone had stolen his new iphone 10 out of his wallet locker - yet his credit cards were still there. I asked him if he used it at all while working out and he said no. Then he said he actually did use it for a text but he put it back - he was sure of it. After looking around another person heard us and said he saw one on the floor by the base of the lat machine that he was using earlier but it was gonzo - figured he put it down between sets and then forgot about it. I told him to go home and try find my phone and if no luck then blacklist it. So he comes back at the end of the night with his laptop as his find my phone says it's still here in the building somewhere. He starts looking around and I go back to the wallet lockers and open up the one above the one he'd had his keys and credit cards in - guess what I found. The look on the guy's face was priceless, but we laughed and laughed.