Part of the problem relates to the Original Cliche of the western novel/movie, as first stated in Owen Wister's The Virginian:"When you call me that, smile!"
On the internet, not only does no one know that you're a dog, no one can tell if you're smiling or not. So things not intended as insults get taken wrongly. Unless you love putting little smileys in your text (which I find rather inane) you have to be very careful not to say anything you don't want taken literally.
This is something I trip up on often, since I tend to use a lot of sarcasm - gently intended sarcasm, but sarcasm - in real-world speech. I assume others have the same problem.
Peter.