A pet peeve of mine and immediate score zapper is when an author not only misuses a word but copies the mistakes of others as proper.
Example: in BDSM stories the abbreviation dom is thought to be dominate. Dominate is a verb whereas dominant is an adjective. The Dominant's toy is dominate(d).
Other misuses -
โข Shutter instead of shudder
โข Collage student instead of College student
And on and on. Arrrgh!