I've been working as an editor for more than a decade now, and there are some behaviors I've seen from writers that I consider disgusting. I'm not talking about not following guidelines, although that happens a lot. I've never edited anything that accepts horror, and yet I'm constantly inundated by it. I'm talking about things like sending nasty letters to an editor after they've rejected your work, trying to sell reprints as originals, slandering editors or publishers because they didn't want to accept your work, and anything else that might be similar.
It might seem hard to believe that writers can act this way, but they can, and believe me, they do! I used to comment on every piece I rejected, but at least once or twice a month I'd get a nasty e-mail back from a disgruntled author, and because of that, I rarely comment on author's work anymore, and that's a bad thing for authors. Feedback from an editor can be a real help to an aspiring writer, but because of a few childish people, fewer and fewer editors are giving feedback anymore.
In a sense, editors and publishers are something like a writer's employers and they should be treated as such. Most people aren't going to call their boss a jerk because their boss wasn't happy with their performance, but since the internet isn't face to face, people seem to have a lot more courage to act like fools.
One thing that writers don't seem to realize is that editors talk to one another, and if someone is misbehaving, there's a good chance that other editors will find out. If your work is rejected, and you're not happy with the rejection, then feel free to write a nasty rant to the publisher...but DON'T SEND IT!!!
Never try to sell first rights to a story that has already been published. It's simply a form of dishonesty, and no one likes dishonest people, plus when you get caught, a lot of other editors will find out, and it could end your career.
And whatever you do, don't go around posting nasty things about editors or publishers because they've rejected your work. You look foolish when you do it, and there's a good chance that other publishers and editors will read your rants, and they'll be much less likely to want to work with you...