I was banned twice from the now non-existent AmericanGirlFan message board. I could still access americangirlfan.com, but my IP was blocked from the board. I discovered the usage of proxies do mask my IP and secretly browse the forum, but I couldn't post.
The first ban was, I guess, understandable. I was venting and didn't really take much notice of the other girls' advice, so the owner banned me for a week.
The second ban was the result of a nasty flame war, of which I was one of four participants. One of my opponents had a long history of annoying and attacking other members, but the site owner took an unusual amount of pity on her and didn't ban her, despite the fact that she had been the catalyst for the flame war (not that the rest of us didn't also share responsibility). My other opponent, who later became my friend, informed me that the site owner went easy on the other girl because she was allegedly autistic. This was before I suspected autism myself.
That second experience definitely taught me to shut up. I've never been very outspoken online since.