Sore Winners and Sore Losers.
Before I get into this, let me explain what they are for those who don't understand.
A sore loser is basically someone who takes losing too personally. Example, they lose and begin flaming their team, the enemy and basically throwing one hell of a temper tantrum.
A sore winner is basically someone who takes winning to the point of obnoxiousness. Example, they win and spam 'ez' or goad the enemy team with questions like 'ff?'
Both are just as bad as the other, both are just as toxic as the other. It's a behaviour that is unacceptable in any scenario where someone has to be the loser. Let me give you an example of a match I had where I was on the same team as a sore winner. It was an ARAM, I was Pantheon and was pretty stoked as I was being able to help my team with a hell of a lot of damage and CC. But lo and behold, we had a Teemo who kept spamming 'ez' despite not doing anything useful other than the odd shroom for wave clear. That is a sore winner. Trash-talks and has a superiority complex. Despite winning it didn't feel good knowing I actively let this piece of shit piggyback off of me.
The point I'm trying to make is this simple request; Don't be a dick.