I'm a <slur>.
Words are bullshit, but we keep using them because they're still too convenient to ditch. Some words take on – or are born into – meanings of sensitive topics, and sometimes those words will themselves become sensitive topics.
"Gay man", "gay Paris", "gay man", "that's gay", and "gay man" are all distinctly different in meaning depending on their context in time, culture, and place.
Words aren't ideas. Words are the _shadows_ of ideas.
I'm a <slur>.
If I call myself a "tranny", I can expect a wide range of reactions:
• startled – "Oh, I thought that was a bad word!"
• neutral – "Not my business what folks call themselves."
• angry – "I heard that word is offensive and I'm calling you out!"
• friendly – "Sisters gotta stick together!"
• confused – "You're, uh... into automotive parts?"
...and so on. But which of these responses is "right"?
I'm a <slur>.
If, after asking for clarification, it becomes unambiguously clear that they're intentionally being hurtful, then give 'em hell, sure.
If it turns out they're just using terms familiar to them, be gentle. Words are habits, and bad habits are very difficult to break. (Good habits are healthy; be open to that possibility, also!)