One

I've always had the urge to tell people about how I'm bi-polar/depressed. Unfortunately no good thing could come of telling people, because they will either get awkward and think you're mental, or they won't really care at all. What I really want is someone to respond  "Seriously? Hmm... Whats that like?" and be interested, just not repulsed. But after 4 years of this, I have yet to meet anyone who would spend more than 2 minuets talking with me about it (except therapists).
Then when someone finally knows about your mental state, they fall into the category's of: Ignorant (clueless about it and why is a big deal) they will often try to forget all about it, Asshole (think you're crazy, a cutter, and always an emotional train wreck) these are the people that will talk about you behind you're back and avoid you. Many people over the age of 35 fall into this category. Then there is a Sympathizer (feels the need to always check up on you) these people often will treat you as their lesser, but they mean well. It's not uncommon for them to "know what you're going through" because their aunt's boss suffers from depression too. They will bring mental health up in every conversation. People like this will often tell others. Rarely someone is a Relief (understands and doesn't make a big deal) These people often have similar mental issues, or have DIRECT experience with it. It's nice finding someone like this because it forms a connection, as well as relives the stress of telling them. Unfortunately its not common to find someone in the same boat.
This is why its so hard to tell people about my illness. Its just not worth the negative. And to be honest its kind of fun (sometimes) to have my own secret.