snit (n.)

"state of inappropriate agitation, fit of childish temper," 1939, American English, of unknown origin. First in Claire Boothe's "Kiss the Boys Good-bye," which gives it a U.S. Southern context. Snitty (adj.) appears to be slightly older.

It likely is unrelated to Middle English snit "glowing part of a wick after the candle has been blown out," which is related to snite.