I don't know what it is. For some reason, the students think that we substitute teachers aren't really there. I know sometimes the students talk like there's no adult in the room. And sometimes they do stuff that they just shouldn't do.
I was covering this computer class (not today, but a while ago). They were working on some project that involved searching for information on the Internet. No big. This one boy was instead working on his English assignment. Again, no big. They know what they have to do and when it's due, so if they feel like another assignment takes precedence, then unless there is a compelling reason to stop them (like a test), I don't.
Anyway, the assignment was about the novel the English class was reading. They were to make up study questions about the various chapters (and there was a shoebox diorama involved as well). What the boy was doing, however, was copying questions off of a study website. He informed me that the teacher knew about the website and had encouraged them to use it. Fine. But the assignment was to make up study questions about the chapter, not to pilfer them from somewhere else. This I explained, but he ignored me.
Somehow I found out what teacher this was for. (See, I ask questions. What's that? For which teacher? I was just curious; I had no idea I'd need the information later.) So, when I got a chance, I called the English teacher and told her what this student was up to (and I gave her his name).
They would call that "snitching". They forget, I'm a teacher, too. (I only remembered this incident because I was subbing for the English teacher today. It's amazing what memories come up when I sub for different teachers.)