Keep in mind that a LOT of people, even otherwise decent folk, have the chance, thanks to the Internet, to be transformed into a seething, raging troll; that wall of pixels can easily obscure and help them forget the fact that on the other side, there's another human being just like them.
Hence, it's also important when playing to keep a cool head, and avoid anything that could provoke them. Simple wording can make a HUGE difference; someone who rages and flames when you tell them "omg u feeding noob" might be the same player who, instead, would respond thoughtfully if you requested they "be more careful, avoid initiating alone, and simply defend and farm for now." (this I've found is the best strategy to help stop a feeder from hemorrhaging and making things worse) Same thing goes in newbie matches when someone takes the lane you'd called already: in 90% of cases a polite "please go (top/mid/bot)" will work, while a "omg noob i already called this lane!" will fail much, much more often.