For Pinoy, RD2, and others, I should clarify, my use of slang such as "rat" is not intended to be derogatory in the least. There are different terms like tattle, rat out, nark, etc. to describe the same action but I do not mean to imply that telling is always a bad thing. Not at all. As for the OP, the three scenarios I gave were all from experience. Of the three, here's what I did:
1. I did not tell on the first person who made the copies. I left that up to his conscience.
2. In the second scenario, I complained to the leadership of the group that I was allergic to cats and had paid money to come to the retreat. I didn't wish to ask the cat lover to reinburse me if I had to spend the weekend in the hospital. I was STRONGLY TEMPTED to tell on the woman for putting the cat in her motel room, because my allergy is so severe, had I unknowingly gotten a room that had even briefly housed a cat, there could have been horrible consequences. I do regret not telling the hotel management in this case.
3. The third scenario was when a newly saved friend thought he'd do us a favor and hook us up to free cable. We did not ask him to do this. I called the cable company and explained that we were getting free cable and they might want to disconnect it as we were not true customers. I did not tell the man's name as I didn't want him to lose his job. Instead, we explained to him that while we appreciated his "kindness" we felt guilty for getting free cable as it didn't seem honest, and had it disconnected. He was surprised, but not offended.
As for narking on BB, if I see profanity, yes, I report it.