Do you want to get under your opponents' skin? Do you want to make your teammates coordinate better? Do you want to gain a level of control over the game that you didn't know was possible? Hi, Billy Mays here- Wait, wrong line. But if you want to learn how to construct the right lines at the right times, you came to the right place.

Let's get some misconceptions out of the way. When I say that the chat box is a weapon, I absolutely mean that, but maybe not in the way you're expecting. I don't mean that you should go into all chat, tell the enemy jungler that their mom is fat, and start dropping racial slurs. That makes everyone hate you (with good reason), it's as unpleasant for your teammates as it is for your opponents, and it's going to get you reported and banned. Frankly, if you do that stuff, you deserve to be banned.

When I say that the chat box is a weapon, I mean that it's a medium for getting inside people's heads, and it can help your team do better than the enemy team just like you doing well in lane or pinging MIA.

The key to a team's success is unity, that sense of team spirit that focuses the team members on coordinating with each other and believing they can win. Naturally, you want your team's unity to be strong and your opponents' unity to be weak. This guide aims to teach you how to use the chat box in conjunction with all the other aspects of the game in order to accomplish this.

If you want your team to work well together, remember this: It's a lot easier to start with a good attitude than get rid of a bad attitude. So start the teamwork early. Start during champ select.

Say something. It hardly matters what it is, so long as it's interesting enough to want to read and doesn't hurt or put stress on your team. It can be anything from an inspirational message ("Ready to win?") to goofy roleplaying of your champ ("MUNDO WILL SHOVE CLEAVER RIGHT UP ENEMY'S ***!") The point of this is to let your team know that you have a brain and you're human. It's easy to forget that the other players are people with feelings. By reminding your team of this, you're setting up for teamwork and success throughout the game.

Say something else when the game starts up. It can be in team chat or all chat, but use the opportunity to establish your presence in the game. Depending on your style, you might continue with goofy roleplaying, give your team direction or information about how you plan to play, wish your opponents good luck, or whatever else comes to mind. Your team is as likely to rally around someone funny as someone who gives good directions and calls MIA consistently. As long as your use of the chat box contributes to their experience, they'll like you, and that's good for when you tell them your big brain plans.

Some things can really hurt your team. If you want to use the chat box well, you need to have some ability to see things from your teammate's point of view. People don't like being stressed and made to feel bad. They HATE being called out. And when it comes to awareness, they're always most aware of what's happening right in front of their face.

Have you ever been called out, or worse, insulted when you made a bad play? Doesn't that just make you mad as all hell? Don't do that to your teammates. It doesn't help them. It only stresses them out and makes them more likely to make mistakes. Show some mercy and learn to hold your tongue when things go wrong. Once you've calmed down, be gentle. Ask your teammates to play safer. Tell them to hug the tower. Ask the jungler to gank.

Make sure your communication is helpful, because nothing destroys a team faster than an argument. When players start arguing, there's very little you can do to stop it as they proceed to viciously attack each other in chat. It's absolutely stupid and can make the whole team lose. The best you can do is avoid contributing to it, though if you're quick and lucky, you might be able to draw the team's attention to an objective that you can all take.

Refocusing your team on important, actionable objectives, like taking dragon, can not only cement your teamwork, but can sometimes disrupt arguments before they've gone too far. Use anything that gets you closer to the shared goal of winning to further develop your team.

Remember that stuff you never want to do to your teammates? Do that to your opponents... but CAREFULLY. You can disrupt your opponents by getting under their skin without throwing insults if you capitalize on your team's successes and your opponents' failures.

You don't even have to be unpleasant. Anything that they learn to associate with something negative in the game can get to them. A classic example is the story of Street Jimmy, as told by Bricky below.
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In this example, Street Jimmy tilted his opponents simply by typing a face in chat whenever he got a kill. Bad thing + rubbing it in = tilted opponents.

Another example is when I stole blue buff from the enemy jungle as Teemo and told their Tryndamere "Thanks for blue buff! :D"

He killed me, then I killed him in the next team fight and took the buff back, telling him "I'll be taking blue back now, thank you!"

The guy rage quit after that.