I once had a flame war with a person on youtube. I remember his name, but I won't say it.
I tried to comment on a video of "Mr. Roboto" because I had never heard the whole song before. I kinda liked it, but made some critical remarks about the video being a little lame or the singing was very anguishy or somesuch. I posted it as politely as possible, and this guy calls me a ****** and I don't know anything about music.
Things got really funny when he used the word "you're" in the correct context, and I congratulated him for it, because a lot of people don't differentiate between "your" and "you're". I was being condescending, but honest. He thought I was being sarcastic, and said that I just made myself look like a moron for correcting him. I said "Yes, I know you used it correctly. That's why I congratulated you."
I was polite every single time. He was a jerk every single time. Needless to say, comments on youtube are hardly ever worth paying attention to.