It's a British English word, so don't use Merriam-Webster [0]:

> a person, especially a man, who is stupid or unpleasant

Or [1]:

> If you refer to another person as a git, you mean you dislike them and find them annoying. [British, offensive, disapproval]

[0] https://dictionary.cambridge.org/us/dictionary/english/git

[1] https://www.collinsdictionary.com/us/dictionary/english/git