If you know you're on tilt, DON'T PLAY RANKED.
This should be obvious but apparently it isn't. This last game, our top laner announced in champ select that he had just been demoted to Gold so he was going to play poorly. Our bot lane duo agreed that they were on losing streaks and would probably lose. Our mid was probably also tilted, but I couldn't tell because he was speaking only in Chinese.
And yeah, I would have loved to dodge if it wasn't the first game of my Gold promos. Top lane went 0/3 in the first 10 minutes to a Riven (who had 4 levels on him at 20 minutes.) I didn't play well either, but for chrissakes, if you know you're likely to lose a game don't queue up for ranked. This shit should be obvious by now, 6 years into League.