I haven't told anyone, besides my T and pdoc (duh) and I told a surgeon once since the medication I take was important for him to know.
I don't want to tell my parents for the same reasons: they mock those with mental illness and throw around the word "bipolar" like it's just any general description and not an actual condition.
When I was in high school I struggled with an eating disorder. It got really bad and I reached out to my parents for help and they basically just laughed at me. All they did was (try to) stop making fun of my weight but they didn't take me seriously and did not get me help.
As for telling friends, I've told a few close ones about depression because it was important to me that they know when I blow off plans or don't want to hang out it's not because I don't like them. But I haven't specifically said anything about depression because I'm afraid of the stigma. I'm sure they would be supportive, but telling people sensitive things about yourself changes the way they treat you, even if just subconsciously.