- Well, it's a good thing you don't see it! The people who see it most often are sex offenders.
- Well, of course you don't see it; you see me only _____ and only one of me shows up _____.
- You don't see it and yet I have been diagnosed with it. What does that suggest to you?
- That's okay, I live with it and I didn't see it myself either for a very long time.
- That's okay, someday you may learn to see it and in the meantime the standard of care does not require you to independently confirm every diagnosis, does it?
- Do you say that about other "invisible" conditions such as cancer, diabetes, anxiety, insomnia?
- Do you mean to imply I don't have it?
- What do you mean you don't see it? Don't you remember _____?
- What do you think it looks like?
- What do you mean?
- Hm, that's odd!
- Really?
- Huh.
I could go on, but you get the point, right? Their not seeing it is not your problem, it isn't even any kind of problem.
Feel free to use any of these that work for you.