what is loshon hara?

I never really delved into learning the halachos behind loshon hara, but I do remember a few things I learned in HS:


1. It is not loshon hara when it is about shidduchim.

2. It is not loshon hara if someone is telling on someone who is cheating/lying or can be damaging towards someone else's business, parnassa or community.


So... with the first one, I don't really have anything to say, because that makes sense, but with the second, there are many morons that just *don't* get this halacha. They're stupid and they judge people too favorably. Therefore, they continue to let the damaging person continue in his bad ways, because they don't seem to grasp that he is in fact harmful to them. One can go on and on telling them about how the said person is bad for them, and damaging, but they just won't listen to you.


There is a halacha that says "Don't stand idly by when the blood of your brother is being spilled"


But when you start saying "dude, he's about to stab you" and they don't want to hear it because it's "loshon hara" are you supposed to go on and on repeating yourself like a broken record? Or are you supposed to stand idly by, point the finger and be like "hahaha, jackass, I warned you!" (I'm so one to do that too :))


Well... by halacha, or my interpretation of everything I learned "YES! go on and on repeating yourself!"


In fact, it happened in the navi (can't remember which), someones was told "dude, they're gonna attack you" and they didn't believe him, because it was accepting "loshon hara" and they got attacked.


The problem is, a lot of people turn everything into personal matters. They think that when you complain about someone, then it's personal. It's *not* always personal. In fact, most of the time, the person really *is* a douche bag.


Many fellow people choose to ignore the obvious (douche bag's presence) just because they choose to consider it loshon hara, or are just blinded by warnings because of money/prestige insentive. But shouldn't you accept the "lashon hara" because it will harm you and being cautious is a form of u"shmar nafshecha" (watching after your life)?.