just lost a game that was 100% winnable because our top 
(ironic right?) decided the game was unwinnable, kept spamming ff, we didn't, so they afkd.
me and my supp won bot, only their enemy mid and jg were ahead.
we didn't lose that game because of our top or mids kda, we lost it because of the bad attitude our top had and refused to play because of that attitude.
I mean... true. Anyone who downvotes this is a fool tbh.
EDIT: I meant the OP not MY post, SMH ya'll are slow as hell sometimes.
nods in agreement couldn't agree more
Yup. I can't tell you how many times I've had someone play a scaling champ and give up after they die once.... it's so annoying.
Well....... yes..... if someone quits playing, that matters more than attitude. But I, as well as others, can have a bad attitude and still try to win. My last game I was playing Sona. One of my Q's last hit 2 minions. My ADC went into a tailspin of accusing me of CSing, he ran down mid and went 0-10. We lost. I developed a bad attitude toward him, but I didn't stop trying.
In short when you think about what causes a loss: Intentional feeding > Leaving/AFK > Giving up > Saying mean things
The funny thing is that in terms of punishments, Riot is more frequent in handing out punishments for "verbal abuse" than intentional feeding.
I'm not sure about majority, or anything even approaching a majority, but sure, plenty of games are lost because of bad attitudes.
