Much in the same way I refuse to play on their turf by calling Nazis and other assorted fascists "alt-right," a term they specifically tailored and introduced into political jargon, I generally refuse to use "TERF" unless it's necessary to refer to something specific. Here, I want to say that I'm not chiding anyone, I just want to illustrate why they're similar situations. I've personally been saying trans-exclusionist and trans-eliminationist. That's what they are.
"TERFs" get rhetorical and political elbow room with this phrase, both because they popularized it, and because they can now claim it's some sort of slur while not having to directly address the obvious implications of their politics and behavior. They want to eliminate trans people, in one way or another on an individual level. If you call them what they literally are, it shifts the Overton window in your favor, just like with the Nazis. Put them on the defensive.
It's fun to riff on it and call them FARTs and stuff as a joke, but to legitimately rob them of their rhetorical legitimacy, you need to label them with the ugliness that they express and wish to enact. Use my terms, use your own, just make sure it's something that they can't use as leverage on their end.
@Zero_Democracy FART is too close to stuff like Drumpf, in both intent and impact. Might've been cute for a laugh for a day or two, but after that it's like the people who still quote Austin Powers and Chappelle.
@Wailing_Oboli Yeah I agree there, I mostly just wanted to be diplomatic.