"troon" is from Something Awful IIRC. From "trans" + "goon" (a shorthand for a member of the SA forums). Not sure how troon morphed from endearing to a slur. The etymology is debated though. I feel like "tranner" (from "trans" + "channer") is usually friendlier.

You probably already know all that. Not sure why I'm debating the etymology of "troon". It's used commonly in chan culture. I feel like TERFs usually use adjacent chans to 4chan, although even then some boards are female dominated.