For the character ask meme: Dib Membrane and/or Danny Fenton :3
A (Realistic): Dib is a lot more like Zim than he thinks, and he would have caused one or more Operation Impending Doom I scale disasters in his younger years if he were given the means. Remember in the Christmas episode when he caused that planet-wide blackout and it only lasted a few seconds because Professor Membrane was standing next to the turn-power-back-on-for-the-whole-planet lever? When Zim did that it became known as Horrible Painful Overload Day and the blackout lasted years! Try and tell me that if Professor Membrane accidentally left the keys in the ignition of the Membrane Labs Giant Stomping Doom Robot, little 5-year-old Dib wouldn't have taken it out on a joyride across the city to go hunt ghost vampires. You can't. He totally would have.
B (Unrealistic and hilarious): Dib hate watches RESEARCHES Earth movies about aliens just as much as Zim does. He too rolls his eyes at how unrealistic they are, but if he came across, say, the one where they make the aliens' heads explode by playing a certain song (Mars Attacks), there's no way he wouldn't get himself a loudspeaker and book it to Zim's house for some experiments of his own. His least favorite movies are the ones where the aliens are good guys. Especially E.T. He can't believe they let the alien get away without dissecting him even a little! Don't even get me started on Lilo and Stitch.
B (Heartcrushing and fun): If he ever had Zim captured and incapacitated, he wouldn't have the guts to go through with killing him... or at least he'd have to get someone else do it for him. Sure, he'd finally have his proof, and there would be no risk of Zim getting away and dooming the Earth... but what if it still isn't enough? Then he would have killed one of the few people that believe him for nothing.
D (Unrealistic but it's my headcanon and I get to pick the movie): Dib hates hugs. And cuddles. Physical affection in general, really, it's always really awkward and uncomfortable. He doesn't even get why his classmates are suddenly into that whole schmoopy kissy holdy-hands thing anyway. Aroace touch averse Dib is what I'm getting at here.