Tip on team morale
When your teammate makes one of the worst mistakes ever... of all time, you just want to insult him/her. With this tip, you can actually insult your teammate without making him or her feel terrible about the mistake. It's actually a very simple thing to do as well!
Now, let's say your Blitzcrank accidentally hooks in the enemy Amumu, and you lose a teamfight because Amumu just ulted your whole team. You might now want to say:
"Blitz, I can't believe you hooked Amumu into our team!"
Well, if we were to say this just as it is, Blitz will feel terrible and start to lose confidence, thus performing poorly due to his now-lowered morale. You've just insulted your teammate, and your teammate will view it as a verbal attack on him/her as you have just called out the mistake.
Now, with this tip, you will add something cheerful to the insult like "rofl", "lmfao," "hahahaha!!" or "xD." As a result, we will have something like:
"Hahaha, Blitz, I can't believe you hooked Amumu into our teamfight! lmfao xD"
Adding something like this will actually completely change the tone of the insult. Because these terms tend to be cheerful, the insult turns into friendly banter! While it may seem insignificant, the tone will change the meaning of what you have said. With the additions, we seem to be cheerfully laughing at something funny rather than sternly calling out a mistake. What this does is make us seem amiable as our teammates will view us as someone who will just laugh off a mistake rather than holding a grudge against it. Our teammates will remember that it's okay to make mistakes and to even laugh at the mistake because at the end of the day, this is a game, and we should have fun playing the game.
Now next time your teammate does something silly like trap you with a Jarvan Ult, toss you into the enemy team, or Bard-Ult you and the entire enemy team, remember to laugh it off in chat with cheerful terms and emoticons.