Use people's overconfidence against them.
This usually happens once a team starts to win.
If you got a good team, you can turn the tables on them pretty easily.
Example: I push and kill you and your tower. I get confidence in going
1v1 with you. And so I get little more cocky and risky knowing I should be able
to get away with it. You can exploit this behavior of mine by ganking me with
team mates, repeatedly if possible. This affects my overall morale and fun playing
the game, because I am losing and I feel so powerless the most likely way to balance
that dreadful feeling is by cussing my team mates for not helping me. Its all downhill once
a player starts feeling powerless in the game they thought were so good at.
Tactic #1: Morale Breaker
Example #2: Its 2v2 in lane battle. Lets say that my team mate is support yours isn't.
If I kill you multiple times whilst not dying because my team mate was healing or shielding me while
yours wasn't doing that or not able to, you will easily go into rage of how bad your team mate is.
This time you will be protecting your morale with the common "unskilled player/noob" blaming that's
in every game. People that are fighting a losing battle are gonna be abusive towards their team mates.
By getting at least one player to start griefing or blaming people in all chat is gonna kill the enemy team's
morale, because that player will only get louder and more annoying with each death of his.
Tactic #2: Divide and Conquer
Play the game, but remember that you are also playing the player.
You can achieve either big or huge success by first defeating the player, then his in-game hero.