One of my jobs is retail and the other is medical, so I have a lot of work-related ones. My biggest one is the people who walk into the store with this nasty look on their faces and the second something takes too long or is out of stock or just doesn't go the way they want, they FREAK OUT on the nearest employee. It's like they walk in expecting to have a miserable experience, so they feel justified when it happens. Along those lines, I can't stand the people that blame Random Retail Peon for whatever they're unhappy about and/or expect them to just ignore policy to give them their way. Sorry, I don't have that kind of power.
Lights left on, cabinets left open, etc. I am always walking by DS's room to see the light on and both cabinet doors wide open. Makes me all kinds of squiggy.
People that mispronounce things, even when they've heard the correct pronunciation two seconds before. I JUST said it!
People that refuse to speak up. I'm working with a guy right now that mumbles everything. All of us once sat down with him and said, "Listen, WE CAN'T HEAR YOU." it didn't help. We have to ask him to repeat every single word he says and he still mumbles. To make things worse, he talks CONSTANTLY so this is an ongoing struggle. That's just rude. I know you are capable of speaking louder.
Judgmental people. Another person I'm working with asked me if it's true Wiccans drink blood then refused to believe me when I said no, asked me about some of my religious practices then talked about why they're evil, insisted that a Muslim imam (except she kept saying "imal" or even "mimal") gave her cousin a magic charm so that's proof that Islam is evil, and has been singing hymns under her breath every time she's around me for the past two weeks. I refuse to speak to her unless I can help it, so she resorts to having loud conversations about converting the heathens with patients when I'm nearby. I couldn't care less about your religious practices, so why do mine upset you so much?