Jerry from Tom and Jerry is, in my opinion, the absolutely biggest asshole from any cartoon. He is usually the instigator in practically most of the situations and just constantly harasses Tom. Anytime that I watched that show, I always felt bad for Tom.
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Tom killed Jerry's family. He ate his wife and children while Jerry could only watch helplessly from his mouse hole. In that moment Jerry swore he'd avenge his loved ones. I guess without context Jerry seems like a jerk, but when you know the truth it's a different story.