I pointed out a couple of things at our workplace that needed to be fixed (I was off the clock and waiting for a ride while they were working), to a person in the affected department who was on duty. They were really easy fixes that they could direct their staff to complete with not much effort, one of which was a safety concern. They got incredibly defensive, snapped at me in front of customers and staff, and walked away from me shooting snark. Had the audacity to go to our location manager to complain about me when I left, when the interaction was on camera and clearly showed them being confrontational while I stood there confused.
The next day, proceeded to barge in and berate me in the office, while I was in the middle of training with my direct report, which left me in tears. They didn't realize that I was in training for a promotion two levels above them, and acted like I was a nobody who should have no opinion, and how dare I tell them something needed to be fixed. I didn't walk around the place advertising my current career path because I'm not a braggy dick, so I guess it didn't occur to them. It was really awkward later when they congratulated me on my promotion, and I didn't know what else to say but thanks even though they had lied about me and tried to demonize me to others.
Turned out they were jealous that I was getting more training time than they were. Because my job was ultimately going to be a lot more complicated than theirs. They had a temper tantrum and complained about this to me when we were alone in the office, and I recommend that they speak to their direct report about it (whose fault they believed this was), because that would be more appropriate than venting to me and they might actually get results from letting their direct report know how they felt. They quit shortly after.