I'm not sure if that is actually possible on any non-heavily moderated forums. The exceptions being those dedicated to these sort of discussions.
I think it could easily be possible. I'm not sure why some people have such trouble with it.
The OCD one seems like people who like to see things in order, like this
Liking that doesn't mean you are ocd, it just means you enjoy seeing things in order. OCD is a hell of a lot more than that, and as someone said earlier in this thread, it isn't something you want to say you have. Actual OCD isn't something pleasant.
So, OCD is usually an example of people who self diagnose. Most people who claim to have it dont actually have it.
I'd like to make the distinction between deciding one has it and self-diagnosing. To decide one has it, one must merely decide one has it. To self-diagnose, one must talk to people who have the issue, do many, many hours of research on the issue, consider whether one's thoughts and experiences actually indicate it or if they merely like the idea, and things like that. Unfortunately, people who just decide that they have an issue, especially OCD, tend to call it self-diagnosis, which makes it a lot harder.