Like most people, I've seen so many instances with lack of consideration, it's ridiculous. There seems to be a surplus of these instances around me. I'll share them in no particular order.
I've been doing work study in the English department of my university since January (well, technically longer than that). Countless students have come in looking for professors's offices. Courtesy says you're supposed to stop at the front desk and ask if the professor is in, or if s/he is busy. Many of the students just saunter in like they own the place. Then when they can't find their professor, the students come back to the front desk and ask when s/he will be available. And I'm reluctant to give them the info because THEY SHOULD HAVE ASKED IN THE FIRST PLACE!
Dear students: What if the professor was in the middle of something super important when you just waltzed in? How do you think s/he would feel about that? How would YOU feel if someone just barged in on YOU? I know you hate it when your parents do it, so why would you do it to someone else?? See? People don't think.
If you make an appointment to speak with someone, it would definitely make sense to be on time for said appointment. Better yet, you should be EARLY, especially if you know for a fact that this person will be seeing a large number of people that day. A young woman came to the office to see her professor. But you wouldn't know that from her behavior. She stood outside the office door and had a rather loud conversation with someone while students inside the office were either finishing appointments with the professor, or waiting patiently for their turn. Finally, after about a half an hour, she walks in to see her professor, who was still with a student at the time.
"Is he behind on his meetings or something?" she asked.
"...No," responded the secretary. "What time was your appointment?"
"3:00." (NOTE: at the time, the clock read 3:05)
I'm hoping you all see the issue here.
Conversely, if you had a meeting with someone that day, and you show up HOURS early, don't expect the person to be there when you are. You can't expect everyone to work with YOUR schedule. You can't get mad because they have other things to do when you show up.
Most of you who know me know I have this thing about smoking. I would never do it, but as they say, "To each, his own". But for the love of higher powers, there are freaking RULES for smoking! You oughta just know you can't smoke everywhere. If there's a sign that says "No Smoking Within 25 Feet", take it at face freaking value! NO, that does not mean "15 feet away if no one's looking", nor will it ever mean "lean on the building so you can look cool". It means "take advantage of this special area we created for smokers like you, 25 FEET AWAY FROM THIS BUILDING."
For smokers who enjoy a ciggy while walking: if there are other people walking, don't blow smoke IN THEIR DIRECTION! It may come as a surprise, but people take great pains to NOT smell bad everyday. Then you come along and ruin it with your puff of deadly vapors, it's just not cool.
Another thing I have failed to understand about smokers is why the choose to smoke in large crowds. Wanna hear some more shocking news? EVERYONE DOES NOT SMOKE! I have even witnessed smokers light up with literally dozens of children hanging around. When exactly did that get to be okay??