Apparently some modern speakers are happily unacquainted with head lice. This lack of knowledge may explain the confusion illustrated by the following examples:
If you want to lose a friend, all you have to do is to continue to nick pick and find fault with everything that they do or everything that they say.
My husband and I nick pick at everything at each other. How can I stop this?
Gamers are great at nickpicking while avoiding actual analysis.
Not sure if I’m only seeing negative stuff or I’m just nickpicking.
What should I do? I feel Teacher is nickpicking on my son.
The verb forms for the actions being described in these examples are nitpick and nitpicking.
To nitpick is to find fault with every little thing, no matter how inconsequential. The expression derives from the literal act of looking for nits, which are quite small. As a former volunteer school “head checker,” I know what it is to comb through a child’s hair, strand by strand, looking for nits.
nit (noun): The egg of a louse or other insect parasitic on humans or animals; specifically, the egg of a head louse when attached to hair.
From the mid-1600s until the late 1700s, ostentatious wigs were fashionable among the wealthy. One of the most memorable passages in the diary of Samuel Pepys (1633-1703) references the pitfalls of patronizing a wigmaker who failed to boil the merchandise before delivery:
“I did go to the Swan; and there sent for Jervas my old periwig-maker and he did bring me a periwig; but it was full of nits, so as I was troubled to see it (it being his old fault) and did send him to make it clean.”
Note: A periwig is a highly stylized wig still worn by British barristers and judges. (The adjective old is not a typo for own. This wasn’t the first time Jervas had sent Pepys an infested wig.)
It’s not necessary to hyphenate nitpick or nitpicking.