Comshipper is an exonym primarily used by antishippers against people who engage in what antishippers have started calling comshipping.
A blend of
complicated ship, comship is a moralist reactionary term which gestures at fictional
relationships betwixt characters that an audience
normal people (normal being ill-defined as the person using the term and the people who agree with them about this), would objectionable when it happens in real life betwixt actual people, and then labels them as
problematic. Tropes that would cause any ship to be labeled a comship vary wildly depending on the sensibilities of the person using the word, but they might include: history of or ongoing abuse andor neglect, imbalanced power dynamics (adult x minor, master x slave, vampire x human, incest), asymetric power dynamics, squicks both common and personal, ignoring the canon, being identifiably queer and/or openly kinky, or being identifiably interacial.
It appears to have evolved from proshipper, where the target of the antishippers' ire has shifted from the too large to easily attack group of people who don't agree with with antis that comshipping is actionably bad to the smaller more specific group of people who actually engage in the comshipping they
disapprove of.
Nobody at time of writing uses comshipping as a self-identifier, though that is likely to change overtime as people attacked by the word pick it up in a definant act of reclaimation.