When people are unnecessarily inconveniencing others for the sake of their own convenience.
For example, my mom broke her ankle a few weeks ago. We were at the doctor's office in the waiting room when she had to go to the bathroom. She was on crutches, so I followed her and helped her open the door. But when we got in, the handicap stall was occupied. The woman who was in there was standing--not sitting--and had all sorts of papers scattered about on the floor (granted, the bathroom was clean, but it was still a bit disturbing).
Furthermore, she was talking on her cell phone. And she wasn't talking about herself--she was talking about her husband, telling the person on the other end about how he was going to get an MRI and whatnot. She was using the handicap stall as her own personal phone booth! So my mom had to hobble into one of the tiny stalls which had no handrails for balance or any extra room for her crutches, which I had to hold onto outside.
Finally the lady came out--never flushed, of course. She smiled at me, and I just looked at her. I made sure I was extra loud and clear when communicating to my mother until she left. "Are you okay in there, mom? How is the FOOT? Do you need your CRUTCHES?" Still the woman was completely oblivious. She seriously saw no problem in monopolizing the handicap stall in an orthopedic clinic in which 95% of the patients are on crutches or in wheelchairs.
I just can't get my head around that. I admit I've use handicap stalls even if I'm not handicapped, but I rarely do it if it's the one of its kind and I sure as HELL don't take advantage of it and do things that can just as easily be done somewhere else. And never EVER in a medical facility if I can help it. It just boggles my mind.
Also, just little things like when people at the supermarket have their carts in the very center of the aisle as people are trying to get by. Seriously, those aisles are spaced to let two carts go by at once, but that can't happen if you've got it parked right in the middle.
And people with large vehicles who park like they're a blind, one-armed lemming. Please note that parking directly on top of the line only makes people MORE likely to scratch your precious blood-red 2011 Dodge Ram, not less likely.