The phrase "splitting hairs" means to argue over small points or trifles, often to the point of being pedantic. It is usually used against a person negatively, such as "You're just splitting hairs at this point, give it a rest."
Phrase Dates Back Centuries
The phrase originated in the 17th century. A 1652 Oxford English dictionary lists the phrase "cutting the hair," meaning the same thing, and lists an example: "Machiavel cut the hair when he advised, not absolutely to disavow conscience, but to manage it with such a prudent neglect, as is scarce discernible from a tenderness."
What It's Based On
Splitting a hair is considered a fruitless and silly exercise. In the 1985 book "The Dictionary of Cliches," James Rogers writes that when the phrase originated, splitting a hair was extremely difficult because of lack of sharp and precise tools. So a person who would split a hair would be a very stubborn and persistent individual, indeed.
Even James Bond Said It
In the James Bond book "Casino Royale," Bond sips a martini and tells a bartender, "Excellent ... but if you can get a vodka made with grain instead of potatoes, you will find it still better." He then adds, "Mais n'enculons pas des mouches." This phrase means "But let us not split hairs" in French.