Lol... are you complaining about someone from these forums?
Oh, no. Sure, some of the people here are slightly like that, but none of them will go out of their way to insult people from their team TO THE ENEMY TEAM. If you type, "Lol, our Morde so pro, 0/11," then you deserve to be shot in the face by a Gangplank. I hope a Garen leaps out of your car. Nidalee spear through your window from that bush outside. Teemo jumps you from invisibility and poisons you, and the end of your life is pure agony as you attempt to flee from that small fellow while pain slowly rakes you. I will feel no sympathy as Malzahar freezes your entire body and pumps endless amount of void energy into you.
I don't care if you spent the entire game telling him how to use a computer, play LoL perfectly, and manage to 1vthe entire game. You don't do that. That is not okay, because you've just destroyed the chance that your team will care about your life. I go out of my way to hinder people like that. If I can heal, I will watch as you slowly drop health, and then heal myself. In front of you. Or I will heal a minion, if possible. Because I could care less about winning anymore. I don't think people like that deserve to win. And I know how much people like that HATE losing.
So, don't be a jerk to your team. If you want, be a jerk to the other team. That way you're not demotivating your team. I try to give compliments when I can in my game, because people LIKE hearing that. They want to know they did well. If your teammates wins a 2v3, give them a "good job!" If your teammate gets killed 1v2, tell them "Try to stick with a teammate if you can" or "Try not to fight them 1v2." If they give you an "ok" then they are doing they're job. Your team is needed to win in most cases, so it's a reeeeeeeally good idea not to make them mad.