Verb: To complain about trivial things, similar to nitpick, but strictly for the sake of complaint. See also, nitbitching.
Noun: Could also mean "a very tiny bitchy person."
"My latte is way too hot to drink. I'm going to have to wait like, two minutes."
"Oh, stop nitbitching."
"I can't believe that midget screamed at you for wearing white after labor day."
"Yeah, what a nitbitch."