During the fight between Jiraiya and Tsunade against Orochimaru and Kabuto in the Search for Tsunade Arc, Jiraiya refers to Kabuto as "Four Eyes". Why did he get that name?
2 Answers
Because he was the only one among all present there that was wearing a pair of glasses.
The term "Four eyes" refers to people that wear spectacles.
I don't recall the scene. But in Japanese, he probably actually referred to him as megane (meaning spectacles). Rather than using literal translations, subbers/dubbers prefer to use equivalent terms which will carry a similar tone in the target language. Since an equivalent epithet used in English for a bespectacled person is four-eyes, that is what was preferred.
Four-eyes is almost always used as a derogatory term in English. But this isn't necessarily the case with megane. That said, considering the character of Kabuto, I expect that that is how it was used in this case. IOW, four-eyes is a perfect fit.