My common courtesy wake-up call: MIT mechanical engineering students often had to go through the course "secretary" to see their faculty advisers of high-level MechE professors. At the time, the course secretary was a middle-aged women with a desk outside of the MechE administrative offices. When you walked into the office, you spoke with her and she would send you to the appropriate faculty office.
Whenever any of my (mostly male) coursemates talked about visiting the office, they always referred to her as "bitch," "cunt," "hag" etc. I never understood this - she had never been anything but nice and respectful to me. After one interaction I witnessed between the secretary and another student, I finally began to understand. Those other students really saw her as just a "secretary" who had no business running interference between students that were clearly her betters. I on the otherhand never went out of my way to ingratiate myself to her, but I did treat her as a human worthy of the same respect as any other faculty member, and I guess she noticed.
One year, I signed up for more classes than I intended to take with the intention of auditing the classes, deciding what I wanted to take and then dropping the excess classes before the drop date. I decided pretty quickly to drop one of the classes, and therefore didn't attend any of the lectures or do any of the coursework, but I procrastinated in getting the signature of my adviser to drop the class.
Eventually the drop date loomed, and I realized I had only a couple of days to get that signature. I walked into the MechE office, exchanged pleasantries with the secretary and asked to see my adviser. "Oh I'm sorry," she replied "he's out of the country for the next two weeks." She saw from my reaction that something was wrong, and I explained that if I didn't get my adviser's signature on the drop form ASAP, I'd fail the class. She smiled and told me that in situations like that she actually had discretionary power to sign forms on behalf of absent professors. She asked for the form, signed it (in her name) and gave it back to me. I was all set. A year after that, I handed in my thesis and forgot to sign a form. She called me and waited after hours for me to run down to the office to sign the form so I could graduate on time. All because I treated her like a human being.
I later told some of my coursemates about that, and they had absolutely no idea she had that kind of power. I like to think that maybe they started treating her a little better after learning what a little courtesy can accomplish. But I certainly learned that "little people" can hold great power that can be wielded in your favor if you just treat them like you want to be treated.