The history of a lot of fandom terms is really fascinating!

Here are some tidbits to get you started and you can learn more on the fanlore wiki!

In February 2018 tumblr user and anti-antishipper freedom-of-fanfic argued that anti is a self-designation. A reblogger commented, “I’ve seen people describe themselves as ‘an anti’ in the meaning ‘I am against pedophilic/incestuous ships and I will actively argue against their right to exist on the internet’.”[18]

Use on 2010s Tumblr
Beginning circa 2016 in Tumblr and DreamWidth fandom, anti-shipper (or just anti) has been used to describe fans who disapprove of a ship and its shippers because they believe the ship is problematic or morally wrong. Specifically, older shippers on these platforms started using and still use the term “anti-shipper” to describe fans who harass shippers for shipping “morally wrong” ships. Having a term to describe the harassers’ ideology became important because fans feared that the harassment was causing a chilling effect on online fandom activity.

An anti-anti is a person who opposes the anti-shipper movement. The term pro-shipper is also used, interchangeably. This term may have arose on Tumblr and/or DreamWidth circa 2015-2016,“[1] with people making blogs to track, expose, or otherwise comment on the behavior and beliefs of anti-shippers. Pro-shipper beliefs are in direct opposition of antishippers. Many pro-shippers aren’t simply pro-ship, but are also anti-antishipper, which is where the phrase anti-anti derives from.