I've only done about 10 duties as this point, and one from yesterday is the only one with a jerk, so it's been okay so far, but even 10% seems too high for me. He ran off one of our players, and I eventually left after apologizing to the healer and replacement, at which point I was the one being flamed.

As much as a voting/kick system seems like it would be good, it would unfortunately be rife with abuse. Since League of Legends has been brought up, I think a Duty Finder Tribunal would be an interesting approach. It could punish by denying the use of Duty Finder for a certain period, meaning they'd have to form their own parties.