A bug that no one has ever seen before that lives in your asshole. At the most embarassing moment, the bug appears out of your asshole, bites you in the back of your balls and runs back in your ass.
Damn that nipdart! To this day I have never caught him.
by Chunners October 29, 2007
The tiny, black, flying insects, usually seen in outhouses, that nip at your nuts and dart up your ass.
Upon returning from the latrine, David exclaims, "I just swallowed a Nipdart and I know it just flew off a log in the outhouse!"
by Hipstr67 May 12, 2016