From 2012 to October 25, 2017, Even someone with whom you have argued for years. Someone with whom you have exchanged countless insults on an unmoderated forum. Or someone with whom you have exchanged the same set of insults over a thousand times.
Interesting question! For sure, we reveal different aspects of ourselves at a joint like this than we do to friends and family. It's hard to know a person very well just through text, though, and what we choose to write and publish for public consumption is bound to differ from what is in our hearts and may become apparent through a personal relationship. We don't know how one another speak, dress, live.. Most of what makes us who and what we are is barely reflected on a forum, I would say. How well do you know an author from his or her published works? These forum discussions are less formal and edited than that, for sure, but still there is a fundamental similarity.
Only online people know my anger. Not only my -- many people use anger and inappropriate language online, which they would never use offline.
I was once booted off a BBC messageboard with extreme prejudice for being too politically incorrect. That's my claim to fame!
This forum likely knows more about my political beliefs than my family simply because my family and I are on completely opposite ends of the spectrum and there is no real "talking" to them about anything political. I've learned years ago to simply not engage in political discussion with any of them because nothing ever comes of it but a heated argument. They all know that I have opposing views than they do but few of them actually understand why because the conversations never get that far.
There are also many issues I do not talk about with my parents. They know my position on these issues very well, but they disagree.