If you're in a public place and spill something, clean it up! Or at least tell someone about it. Yes, it is probably someone's job to take care of those spills, but don't just walk away from it. Someone spilled Cheerios on some stairs that don't get used very often in my office building. They stayed there for days! I know, I know, I could have said something. But I still blame whoever spilled them.
Pick up after your dog! Even though I'd really prefer that you not let your dog do any business on my grass, I recognize that they have to go somewhere. So if they do end up leaving anything behind on my lawn, you need to pick it up. And if it's your kids who take your dog for a walk, you don't get to blame it on them. You're responsible for your kids too. Scalawag.
If you see someone with their zipper down, food in their teeth, something hanging from their nose, etc., you have a moral obligation to tell them. You really, really need to do this. I am tired of always having to be the one to tell people. It doesn't matter if it's your boss, an annoying co-worker, or the Pope. If you've ever had someone discreetly let you know that you have a button undone, you're forever grateful to them. If you come home at the end of a long day to find spinach in your teeth that's been there since lunch, you hate everyone you talked to that day. Don't be that hated person.
If you need something, ask politely. Don't just declare your need. It makes you sound needy. As you may know, I work in Human Resources. I regularly receive requests from employees to fill out forms or prepare letters for various things. It amazes me how often I get emails that say something like, "Rob, I need a letter verifying my employment so I can establish residency." I'm always tempted to just write back and say, "Okay, thanks for letting me know." It's like when my kids say, "I'm hungry." My response is usually a variation of, "Oh, that's interesting. Thanks for telling me."
When using instant messengers at work, don't just say, "Hi," and wait for the other person to respond. Tell them what you want. The great thing about instant messaging is not having to engage in small talk. Stop doing it wrong!
When leaving a voicemail message, give some useful information. If all you say is, "Call me back as soon as you get this message," I will most likely ignore you. Also, don't tell me what to do. Also, don't call me when an email or text message will suffice.
Don't tell someone else to remind you of your commitments. This one really baffles me. If you say you're going to do something but are worried about forgetting, put it on your own calendar or set up your own reminder. Don't try to defer accountability to someone else just because they are more reliable. Organize your life!
These things literally drive me up the wall. I could go on, but that's probably enough for now. Feel free to add your own observations in the comments.