Ha, I had a teammate rage quit today, but that guy was a nutter. It was 2v2 Team Favor and things are going well, we're slaughtering away and I think everything's fine. Then his mic flips in and he starts ranting and raving about me "stealing his kills" and how we need to keep the kills even or we get no score and by me getting all the kills we're not getting points.
Mind you, my "stealing" was saving him from the brink of death by killing both of the other team or interrupting an enemy's combo that he was caught up in. I was using the Blade of Hades, too, it's not like I have a lot of precision with L1+square.
So then I just started standing by and let him get rocked without my unwanted intervention, that way he can get all his awesome k1llz! Not surprising, he got worked over and then started complaining that I wasn't saving him.
I was having a pretty good laugh at that point. I jumped back in and we won soundly. Post-game I tried to explain to him it's a team game, there are no his kills and my kills and if the enemy keeps dying and we keep living, we get points. It's pretty simple.
He didn't seem to get that and kept blathering on about not getting points and my rampant thievery. I let him get beat up some more, which prompted, "Have fun on your own! I'm leaving!" I then did have fun.