I'd say Misty. Iris just picks at anyone and Trip is the least meanest of them all. Saying someone's a boonie isn't mean it just means he needs to start thinking better. So I guess he and Iris are the same. But Iris told Cilan, Georgia, Burgundy and Ash, so that's just over doing it.
Paul being the meanie is just a fact.
Paul was not giving a Damn thing to ash
While I wouldn't necessarily say she's the meanest overall, Misty wins easily.
Physically abusive, very rude and such to Ash. She was harshest on both fronts.
None of the other characters really compare to Miss Tsundere.
Setting him on fire trumps all.
Charizard is the epitome of mean. The guy goes as far as to burn his own trainer.
Paul didn't seem to give a damn about Ash and neither does Trip now, but I think Trip's a little more toned down. Just a bit.
Gary's a jerk to Ash, and he picks on Ash automatically(Gary was here! Ash is a loser!), but as least he seems to gain a bit of respect towards Ash after Ash defeats Team Rocket at the Viridian Gym.
Iris is a total brat towards Ash and puts Ash down the chance she gets, but she can be a brat towards anyone. Misty, on the other hand, seems to love picking on Ash exclusively and even physically abuses him. But we all know she cares deeply for the guy.
I say it's Paul!
Paul was the biggest meanie because he always picked on him and called him names (he should have told professer oak) haha
I put Paul, for one reason: the truth is a harsh mistress. That is what makes Paul a good rival, he has a point. His methods are effective, and far more efficient than anything Ash can do. To even further punctuate the point, he even deconstructs Ash's entire strategy and reveals his true character flaw: his recklessness. He put Ash through the toughest challenge up to that point. It's a pity that Ash did not receive any real character development for that, but him and Paul had an excellent battle at the end. He makes all other rivals seem like small potatoes in comparison. (Unless you include Tobias, but there is no dynamic to speak of there)
I would have to say Paul, as he was more or less a jerk to everyone, let alone Ash, even his own Pokemon were victim to his jerkassery.
I don't understand how Misty, or anyone else for that matter, could be meaner than Paul. At least Misty was mostly teasing with Ash in a friendly way, it's not like Ash got very upset about it. Paul, on the other hand, truly angered Ash and really frustrated him, and I'm not saying that was a bad thing since that was a key element to their awesome rivalry, but truly none other could've been meaner to Ash. He meant what he said when he said that Ash was pathetic.