While Vegeta may be one of the greatest heroes in the Dragon Ball universe today, there was a time when he was a vile villain of the highest order–and his worst crime of all was committed against his wife and son.
Vegeta was introduced in Dragon Ball chapter 204 by Akira Toriyama when he and a team of Saiyans descended upon the Earth in an attempt to conquer it and kill every living thing on the face of the planet. Vegeta was the leader of the last remaining Saiyans in existence, and while he and the rest of the Saiyans under him worked for Lord Frieza, Vegeta was determined to put his Saiyan strength to the test and defeat the evil emperor who had claimed ownership over his life. In that effort, Vegeta committed a number of atrocities, including killing an entire village of innocent Namekians for a single Dragon Ball and killing most of the Z Fighters on Earth for that very same reason–and that’s just to name a few.
In Dragon Ball chapter 347 by Akira Toriyama, Vegeta had just decimated Android 19 and was hunting down Android 20 aka Dr. Gero after 20 ran away from the fight following the death of 19. When Vegeta found him, a private plane was flying overhead containing Bulma and her newborn baby, Trunks, who was also the son of Vegeta–and Dr. Gero used that to his advantage. Counting on the Z Fighters’ heroic nature, 20 shot down the plane and flew away in a flash immediately following the chaos he had just ensued. Rather than making any effort whatsoever to save his son and wife, Vegeta took off after Dr. Gero as he was hellbent on killing him, because doing so–in Vegeta’s mind–would confirm his Saiyan superiority.
While it could have been argued that Vegeta was just mission-focused and went after the greater evil in an effort to save the world, that argument is completely put to bed after he explicitly states that he doesn’t care whether Bulma and Trunks live or die. When Future Trunks, who joined the fight a bit later, watched the inaction of his father, he became enraged that Vegeta would allow those closest to him to die without lifting a finger. What’s worse, is that Vegeta at this point was a Super Saiyan, which meant he had the strength and speed to save Bulma and Trunks and then go after Dr. Gero without losing any ground. Essentially, Vegeta could have saved them like it was nothing, he just didn’t want to.
Vegeta has done some terrible things in his past, but committing acts of evil while in the service of an intergalactic tyrant is a far cry from watching his family die in front of him and not caring in the slightest. It is one thing to be a world conqueror or to kill strangers in pursuit of eternal life, but to let people so close to him die needlessly is truly evil, especially when it would have been incredibly easy to save them–proving that Vegeta’s worst crime in Dragon Ball was against his wife and son.