1 - Nobody can fight with someone who won't fight back. Therefore, if you don't want to fight - don't.
2 - Tantrums are a bid for attention. If you don't want the tantrum, don't reward it with attention.
3 - You can't control other people - what they think and say, or how they act. You can only control how you respond. No response is an option.
4 - Having the last word, if it's not a good word, is just being the last jerk.
5 - You catch more flies with honey than with vinegar. It is entirely possible to be assertive, even demanding, while still being a courteous adult. You can even express a whole boat load of frustration with dignity. If you want your message heard, keep attention on the message and not on your delivery.
6 - Extreme anger has more to do with the person feeling anger than the issue to which it is attached. This one I didn't learn from my Mother - I learned it from the recovery crowd, Christy's therapist, her psychiatrist, etc. If something makes you jumping up and down mad, something that is just not that important in the scheme of your life, it's time to look at your life.
Anger hurts - physically. The person most hurt by anger is the angry person. High blood pressure, lowered immune response... It's pretty well documented.
When we post over-the-top anger we volunteer to ramp up those ill effects for ourselves. It's not a stretch that the flamer intends to inflict that on the target, which is childish at best. Worst of all, at least some of this anger spills over onto other readers, who just set out to read what sounded like an interesting thread. Even when you discipline yourself to click away, move on, etc - there's still that little zing, 'cause none of us is actually Buddha.
7 - Making amends will free your soul. An apology, when appropriate, is the gentle art of forgiving yourself for a misstep, redefining yourself as the person you wish to be, and inviting others to view you as your best self.
8 - An apology with a "but" attached is not so much an apology.
9 - Measure twice, cut once. Hmmm - on this forum I would rephrase as "Read three times, draft twice, post once". We've all done it, myself included - read something and smashed off a reply without taking the time to understand the question, check whether we're reading things in that are not there, etc.
10 - Other people's points of view are valid. Just because you don't agree doesn't make them automatically wrong. Just because their post has some anger, doesn't mean the premise is invalid.
11 - Two wrongs still don't make a right. Responding to a post you think is rude with one that's also rude is just extra rudeness.
The good news - amends are always an option! Really. A sincere apology is phenomenally freeing. Entire nations have had wars, called a truce, helped each other rebuild and become friends.