I used to be a mail carrier, so I've got a few stories I could share.
There was the 95 year old retired Army vet who would give me a bottle of wine as a tip at Christmas. The first time I met him, he was writing his name on the top of his mailbox in sharpie, and when I asked why, he said, "Because the doofus you have delivering our mail keeps mixing up the boxes," to which I responded, "Well, as that doofus, I apologize, I just started" and he started laughing and apologizing. He'd greet me from the porch every day with his mug of wine and a hearty "Oh boy, here comes trouble!"
There was the house that refused to empty their mailbox of mail, they'd only take packages. I took all their mail from their full box like 3 times over the course of six months, making them come pick it all up, and they kept doing it. So, one day, I had two small packages, and their mailbox was 3/4 full. I knew if I just threw the packages in there, the packages would be grabbed and the box would be full of mail the following week.
So, I pulled all the mail out, put the packages in the very back, and put all the mail back on top of it. She called the supervisor at the post office saying they weren't on her back porch, he told her the packages were scanned delivered and they should be there, check the mailbox. She called him back and said the mailbox was empty. He told her he'd contact me and figure out what happened.
He called me, and asked where the woman's packages were. I told him this was the house that wouldn't empty their mailbox, so, I put them under all of her mail to try to force them to take their mail. He laughed and told me when I got back later that she had called back and said she still couldn't find them despite "looking in the mailbox," and he simply told her to empty it and she'd likely find them.
Had a house that kept leaving their dog off leash, and it would run up and bark at me while I was walking around their neighborhood. Per USPS policy, if a dog is outside and loose without any kind of fence/leash/etc, then the neighborhood doesn't get mail that day. I told the kids they needed to keep the dog inside, I told the mother, I told their neighbors, and I was working the issue with my postmaster. The PM called them twice and sent them a letter telling them the dog is either inside when I pull up, or we're not delivering anymore.
Well, I got one house past the dog's house, and it came sprinting out the front door, barking and running for me. I'd had enough, and I snapped. I stomped, stood my ground, and shouted at this dog and it just stopped and started running back. Their son was in the yard, and (I feel bad in hindsight about it) I kinda yelled at the kid, telling him that damn dog was supposed to be in the house, their parents knew this, and they were lucky I didn't dog-spray the little shit (the dog, not the kid). Whole time the kid is frozen, a yard away, just staring at me.
I continue walking my loop, still irate, when I see this guy starting to walk towards me, asking me why I was yelling at his son. I turned and asked why, after all of the warnings and requests they'd gotten, they couldn't keep their fucking dog inside for 15 minutes a day when I'm here. He followed me on my loop, kept asking me to stop and talk to him, as we're shouting at each other all across his neighbor's lawns. I just kept telling him I had nothing to discuss with him since him and his family clearly couldn't listen, and I strongly encouraged him to call the post office.
So he asked for my name, and I told him "Dave, no need to write it down, I'll be letting my postmaster know you and I spoke," and left. When I got back to the office at the end of the day, I was pulled into the office and handed a stack of letters from my postmaster. "You're to deliver all of these to that neighborhood tomorrow, this is the 4th instance of that dog being loose, the whole neighborhood is going to the curb." (This means moving the mailboxes from the house to the road) Well, the neighbors absolutely lost their shit that they were being forced to move their mailboxes because of their irresponsible neighbor, even asking me about it as I would go through the neighborhood.
To end on a slightly lighter note: the reason I told the guy my name was "Dave" was because it was the unofficial response for our office. We had a carrier named Dave that was kinda the office punching bag (he took it well and gave it right back). The old timers told me that years ago, one of the carriers Scott (I think) got into with a woman on his route. Like, in each other's faces, shouting, cussing, etc, it was heated. Well, when the woman asked for Scott's name, he said, "Dave!"
Dave got back to the office that day, and the PM is laying into him about how he was speaking to this customer. He's shouting back at her that he has no idea what she's talking about, and she keeps insisting the woman said the carrier's name was Dave. She checked the address, and it wasn't on Dave's route, so then she started yelling at him about why he was so far from his route (this was before the GPS-enabled scanners). All the while, Scott is laughing his ass off in the break room listening to all of it until they realized and started yelling at him, haha.
Last one (again, not my story, but another from an old timer): Back in the 80s/90s, the post office was a different beast: no GPS tracking, no cell phones, if management wanted to observe you work outside the office, they had to either find you or ride along with you. Because of that, carriers used to do all kinds of stuff back in the day that you can't now (like everyone finishing their routes by 11 am, and then all going to the bar until 3 before heading back to the office).
Well, this one carrier had one of the "rough" routes in his city, but he was always treated well because he brought the government checks every month. Well, his customers knew when their checks arrived every month, so on that day, he'd park at a bar at the end of this long street, and just drink his beer while the customers came through and got their checks. When everyone from that end of the road had come through, he'd drive to the bar at the opposite end of the road and repeat, since everyone had just watched him drive by. And they'd all cycle through, all while he sat on a stool, drinking his beer, and making his bread for the day.