I think it either comes from frustration in a game, mob mentality or rebellion.
1. Let's say you're playing Pac-Man at age 5. You can't even get a Power Pellet. You try again maybe 10 years later. Still can't. This causes you to think negatively about Pac-Man.
2. If a lot of people don't like Pac-Man, you'll want to fit in and go against Pac-Man too.
3. Alternatively, maybe you want to be different and spew hate about Pac-Man while others enjoy him a lot, to rain on their parade.
Also, don't you dare touch Geno. He's got as much as a chance as Pac-Man in my opinion. Of course, I'd like him as a second-party with his own series, since Nintendo co-created him (similar to Pokemon, EarthBound, Kirby and even Waluigi), giving us the Fab 4 Third Parties (Sonic, Snake, Mega Man and Pac-Man) alongside Geno would be the greatest birthday present ever (PLEASE be released April 27th, PLEASE be released April 27th
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