I'd rather see a downvote system actually. I can't imagine I, or others, will constantly upvote people every single run just because they weren't a jerk. But if I can right click someone and there's "downvote for jerkness!", sure. Also, since an upvote system provides rewards--which are just cosmetic and so many people don't even care--, there's no incentive to still not be a jerk. If too many downvotes puts a lockout timer on all dungeons for however long, now that's an incentive.

Of course, that can also be abused, so I don't even know how I feel about that.