Manners.

Today my day was made worse by bad behaviour.

One pupil turned up half an hour late for his oral exam that's part of the school leaving examination. So, important date, one of four big exams that determine your future. You'd think you'd be punctual for that.
He didn't apologize, just the opposite, he insisted that he'd read the schedule and the fault wasn't with him. Well, he misread... He still got to do his exam, even though it cost me thirty minutes of pre-planned time with the photocopier.

Then one of my advanced classes, one year away from the above exams, got lost on the way to our new classroom. (We'd had to change rooms and buildings because of the exams.) It was a really bad case of peer pressure coupled with extreme silliness - they've got this game where the first person to walk through a door or a gate is declared persona non grata though they use a term that is a lot less nice. So, they all stood in front of the school gate and would not budge. No one wanted to be 'it'. I'd walked ahead and hoped that they'd follow. They didn't. After a couple of minutes in the new classroom I investigated, maybe they didn't remember the room number I'd given them? and they still hadn't moved. Some were sitting on the pavement. They got an earful - I basically told them that after this display I wasn't prepared to teach them for the rest of the lesson - and yes, that might be construed as just what they wanted to hear - and I retreated to the staffroom, furious. They turned up later and apologized. I collected their homework, which more than half of them hadn't done. I accepted their apology, which was more than we got from guy who was late.