Okay, as a Dragon Ball fan(boy), I gotta point out that he didn't kill Nappa for no reason. He killed Nappa because he was useless. Goku didn't simply beat Nappa. He broke Nappa's back and paralyzed him from the waist down. Even ignoring that the "low class" warrior of Kakarot just made sport of the "Elite" Nappa, he could no longer fight. Nappa was a saiyan that couldn't fight and that made him useless to Vegeta.
I blame Supreme Kai for Buu way more than Vegeta. He knew nothing about some of the most powerful beings in the universe. Goku, Vegeta, and Gohan were way stronger than he realized, and it makes me wonder if his boast that he could have easily beat Frieza is even true. Besides, if he could have beat Frieza, why the fuck didn't he? I'm sorry a Galactic tyrant with a hobby of genocide is not a big deal? Let's not forget that he allowed Spopovich and Yamu to drain Gohan and almost kill him. And they got so much energy from this that Babadi was half way to restoring Buu. Without that, Majin Vegeta fighting Goku wouldn't have revived Buu before Gohan and Supreme Kai could stop his revival.
There's an idea for a list. 8 ways Supreme Kai is a complete moron.
As for destroying the Potara Earrings, Goku didn't really wanna use them after they freed everyone from Buu, either. Like Vegeta, Goku strives for challenges and worthy opponents. And he didn't really wanna fuse again. It's not like he couldn't have taught Vegeta the Fusion Dance if they really wanted to fuse. I mean other than the rampaging pink bubblegum monster that probably wouldn't have allowed it, but... y'know.
Tarble is possibly canon (not sure what the official word on that is), but he's also very weak. He's kinda like Gohan. He isn't a fighter. He doesn't really have the fortitude for it. He's basically Saiyan Chiaotzu.
As for the Planet Vegeta thing, that was their home planet. And King Vegeta didn't so much as pick a fight with Frieza as he made a last ditch effort to save his people. Frieza had already decided to destroy the planet before that. In canon, he ordered all the saiyans to return to the planet specifically so he could kill them all in one go. Besides, the saiyans were terrible. They were arguably worse than Frieza. Maybe they weren't as strong as him, but they could easily conquer whole planets with just a small force. Should we really be upset that a race of murderous, planet conquering, supermen died?
I really only feel like he really screwed everyone over with Cell. And, yeah, he screwed everyone over good with that one. Most of the others are more for reasons of plot.
A fun list, though. All hail the King of Screwing Everyone Over!