Being interrupted when speaking. I'm not talking about completing someone's thought, or accidentally thinking they were done. Accidentally is fine, accidentally happens. Some people are more concerned with their opinion though, and voicing their opinion than the actual conversation itself. I consider myself to be a pretty calm person, but making a habit of inconsiderately interrupting me is a quick way to get me irritated with you.
People who cannot properly logic.
People who mix religion with politics, or religion with law, or medicine, or really with much of anything.
Being able to find clothes I'm alright with, but not any that I love. All the ones I see that I love are one or two sizes too small for me. I know I'm fat, but even once I lose that I'm still going to have a height/build that makes clothes shopping just a disappointment.
Friends who treat me like a Savings & Loan. I don't make that much more than you. Depending on the friend, in many cases I make less. I really don't make much at all. I just know the difference between treating myself now and then within my financial means and pissing my money away. I hate being the jerk that turns down a friend when they ask if they can borrow a few bills to take care of something, because I know most people don't ask easily, so I tend to give the benefit of the doubt unless I know I either can't rely on them to pay me back or if the situation is brought on by their own irresponsibility. What really irks me is when paying me back clearly turns into a backburner issue; like hey, here's twenty bucks toward that three-digit debt, I'll get you again later(three-four weeks, IF I remind them. Longer if I don't.) I'm not some credit card you make your monthly payment to, then go out to the bar. Maybe I'm the anomaly here. Maybe I'm the one that's different, but for me, in the few cases I've borrowed money from someone, that debt turns into an immediate thing I take care of following the necessities; bills and groceries and such. Like, in my mind I don't have fun money until that's taken care of. Someone did me a favor. Simple as that.