WARNING: The following article contains spoilers for Dragon Ball Super Chapter 76, by Akira Toriyama, Toyotarou, Caleb Cook and Brandon Bovia, available now in English through Viz Media.
During their bout with Granolah, Vegeta had a sudden return to form and began turning on Goku. While it wasn't nearly on the scale of his turn during the Buu Saga, it was still a major point of the fight. Vegeta's pride was more at stake here than anything, and having Goku save him was a kick in the ego for the Prince of Saiyans. It's totally in character for someone like Vegeta.
Back during the Buu Saga, Vegeta also had a turning point, allowing himself to become a puppet of Babidi. Under Babidi's "control," he blew up a stand of spectators, almost hitting Bulma, in a bid to get Goku to fight him one-on-one. Dubbed Majin Vegeta, he was able to match Goku blow-for-blow. He explained that he allowed himself to be turned because he believed having ties to Earth made him weak and that, by joining Babidi, he would return to the way he once was. His Saiyan nature was conflicting with the person he had become.
However, this was all a lie to get Goku worked up. When the two halted their fight to take a Senzu Bean in preparation for confronting Majin Buu, Vegeta knocked Goku out and took the Bean for himself. He planned on fighting Buu one-on-one, taking himself out as well in a suicidal bid to atone for killing so many people. He has one last moment with his son Trunks, telling him he's proud of him, has Piccolo take Trunks and Goten somewhere safe, then uses Final Explosion to blow himself up, hoping to take Buu out at the same time. Unfortunately, his attempt was in vain, as Buu regenerated after the attack.
Vegeta's penchant for turning against Goku is in character for him. It's all down to pride. In the Buu Saga, Vegeta allowed Babidi to think he had control of him because he believed the power increase he gained would be enough to take on Buu alone. He challenged Goku to see how large of a power increase he received, because he knew Goku was stronger than him. It was a way to gauge how much stronger he had become. Vegeta knew that Goku would use the Dragon Balls to revive anyone he killed. He knew Goku would refuse to fight him unless provoked. He didn't want to rely on anyone else to protect his family.
In the Granolah fight, he even says that the one reason he teams up with Goku is to protect his family. However, in this case, the only thing in peril are his and Goku's lives, and Vegeta would rather die fighting than rely on Goku to protect him. He even resorts to saying "please" to Goku to fight Granolah alone. He knows that he can get Granolah worked up because he also lost his entire race. He takes the pain he felt and channels it into sharp-tongued vitriol, saying that Granolah's mission is just repeating history.
Vegeta's turning against Goku has always had a bigger role in the plans he concocts. It's his way of telling Goku that there's something pushing him to go to extremes, and that he wants to do things on his own. He isn't someone who outright expresses his feelings, instead relying on his actions to do so. Goku knows this and understands that, when Vegeta hits him from behind or does something incredibly destructive against him, there's meaning to it. Fighting is his way of communicating his feelings, and it should happen again. It's great characterization for someone like Vegeta.
