In the early chapters of Dragon Ball, Krillin was nearly successful in killing Vegeta after the villain threatened to decimate the Earth–and seemingly because of this, Vegeta enacts horrific vengeance against Krillin in a way that is utterly irredeemable.
Vegeta and Krillin first crossed paths during Dragon Ball’s Saiyan Saga when Vegeta and Nappa invaded Earth with the intention of eradicating all living creatures on its surface and selling the vacant world to the highest bidder. After Goku tried to stop Vegeta himself, Goku was severely weakened, so he passed his remaining energy to Krillin, and he used this power to great effect. Krillin nearly killed Vegeta with Goku’s last remaining energy, and when Vegeta crawled back to his ship, Krillin almost finished him off for good with Yajirobe’s sword–and the only reason Krillin didn’t kill him was because Goku pleaded for his life.
In Dragon Ball chapter 382 by Akira Toriyama, Vegeta had just proven that he is stronger than Cell while the villain was in his imperfect second form. Cell had already absorbed Android 17, and he still needed to absorb 18 in order to unlock his perfect form. Since Vegeta wanted to know he was stronger than Cell at the villain’s best, Vegeta told Cell that he wouldn’t stop him from absorbing Android 18. Not only that, but Vegeta actively prevented anyone else from trying to stop Cell from reaching his final form, including his own son, Trunks. In the end, Vegeta’s plan to let Cell unlock his perfect form is successful, and Vegeta's able to fight him at his strongest.
The Detrimental Impact Vegeta’s Hubris Has On Krillin
While this entire chain of events mostly plays to Vegeta’s pride and ego, there is also another aspect to Cell absorbing 18 that Vegeta enjoyed just as much. Right before Cell’s assimilation of 18, Krillin had the chance to deactivate the Android with a device Bulma made so that Cell couldn’t take her power for himself. While Krillin almost pulled the trigger, in the end he couldn’t do it as Krillin had feelings for 18 that he made clear before everyone at this moment. So, when Vegeta allowed 18 to be killed, Krillin was absolutely crushed–both emotionally and physically.
After Cell absorbed 18, Krillin attacked the villain in a blind fit of rage and sorrow–and that went about as well as anyone could have guessed. Not only did Cell take zero damage from Krillin’s attacks, but he nearly killed the hero with a single move right afterwards. Cell demolishing Krillin without even trying right after absorbing the woman he loved acted as Vegeta’s perfect retribution. Again, Krillin almost killed Vegeta with a sword when they first met, and no one would have brought Vegeta back to life if Krillin had done so. So, while Vegeta didn’t originally intend on getting revenge against the man who almost killed him, he certainly wasn’t upset when his act of hubris resulted in Krillin’s unparalleled turmoil–the ultimate payback for what Krillin did to Vegeta so many Dragon Ball chapters earlier.