I think that all humans have pet peeves of one form or another. Some are just more bothersome than others, at least to me. My worst one is when people are late. It irritates me to no end.
I try never to be late. In fact, I've always been that one even when I was very young. I didn't like being late for anything. I was often early wherever I went. I always felt it was better to be early than to be late. Especially if I was meeting someone and had told them a specific time to be at a certain place. I felt it was rude to tell them I would be there at a certain time and then stroll in late. I still feel that way. If I tell someone I'm going to be somewhere at a certain time, I will do my best to get there before then or at least right on time. If I'm going to be late, I call or let them know, so they can either wait or carry on with their time.
It irritates me to no end when someone makes an appointment with me or a date for something, give me a certain time to bet there and then shows up late. Worse yet, is if they do this and they don't call or try to contact me in some way to let me know they will be late. I had this happen just today and this was for a work-related meeting. I had to contact this person to find out what was going on after they didn't show for almost 20 minutes and then was told they were running behind and would contact me when they had time. Livid. I was livid.
Time is a very precious commodity. I have learned that it goes away very quickly and once gone you can never get it back. When someone schedules something with me, I expect them to be there or at the very least let me know they will be late or won't be there at all. It's not too much to ask I don't think. This way, if I do have something else I need to get done, and believe me I always do, I can take care of that while I wait or the event can be rescheduled and I can go on about my life. I have a friend who is perpetually late to EVERYTHING we ever do together and as such, I have started showing up later than she says because I know if I show up on time and wait for her I will just get irritated about it. But, her patterns I know. People I don't know that well or who haven't been late previously, I will be on time or early and then trouble starts.
Some people tell me to just relax and let it go, but I just see it as too rude to let it pass. I don't do it to others and I expect them not to do it to me. Maybe I'm just expecting too much out of people.