Vance was the most embarrassing. He yelled at a dully elected foreign head of state. Zelensky did come across as entitled and arrogant, but having said that Trump and Vance shouldn't have retaliated the way they did. It's not only embarrassing, but this event could make other Heads of State less willing to engage in diplomacy if they know they are going to be berated like this.
No one is going to trust the U.S. now. It's reminiscent of when Vercingetorix of Gaul intended to surrender as an equal King to the Roman Emperor Julius Cesar, only for Cesar to disgracefully ignore his status and throw him in prison. The Oval Office meeting was not quite that bad, but it's always a dark road to go down when stuff like this happens in history. Diplomatic meetings are supposed to be peaceful for this reason.
I doubt that this was a setup by Trump, Vance, and the Republicans as some have suggested. Seems too unlikely. They even had an expensive lunch that was planned after Zelensky signed the mineral agreement, but after the incident he refused to sign the agreement and there was no lunch. Instead it's likely that Trump and Vance just reacted as they normally would because they both are; easily provoked, won't listen to any compromise, insist on being right despite evidence to the contrary, insist on looking masculine and domineering, are rattled by the slightest provocation, and have poor temperaments for leading a country overall.