I am almost NEVER completely open and honest about my DC, even with my closest, intelligent friends with children (who are also probably very bright). My reason is trying to avoid hurt feelings and envy.
Still, my DC have said things spontaneously in front of others that usually lead me to go into big time "downplay it!" or "humor mode."
I cannot help but try to put others at ease about it - I learned the hard way after being mocked as a child for simply speaking. My "friends" proceeded to mock my vocabulary. I learned to use slang and poor English at times to fit in. I also learned that I had to be careful about who I was with when truly "being myself."
Yes, I have walked away from a few conversations quietly chastising myself for being "too honest" (but usually not completely honest) about my DC.