The acronym TERF—Trans-Exclusionary Radical Feminist—is not a slur, any more than “fascist” or “convicted pedophile” is. They are all plain, declarative descriptors for deplorable people.
You’re free to pretend that TERF is a slur, if it feeds your inner need to feel persecuted without actually being disadvantaged. However, the rest of us do not need to respect your martyrbation fantasy.