Here's how I calm down AND stay calm in the futre. It's a cognitive exercise so bear with me.
Here's a question, how could it be personal if you don't know this person. If he struck a nerve then it's effect is more to do with you than him. In fact nearly all anger can be traced back to you giving vent to something that's already making you angry, whether this person said anything or not.
Sometimes people can just be ignorant and offensive. That's what the internet is for unfortunately. They can say and do what they like and trying to "outwit" trolls can be difficult, pointless and dangerous (getting banned from sites). Knowing those morons are there is the only armour you have. Keeping that in mind next time you get angry might help you see them as a sad troll.
But generally the best thing to do is ask yourself "Why does this 'thing' bother me so much?" Most anger is a reflection of how we see ourselves. Getting jealous, bitter, angry, or resentful towards strangers (on the forums, in the media or just walking by on the street) is a big signal from you subconscious that somethings bothering YOU and it's not that person.
Case in point. Ever find yourself getting annoyed at a "type" of person you see on the street. I'm not talking race or anything, god forbid, but you know some chav, or emo, or overly loud person, or suit wearing person. These aren't mine just the types I've seen people hate on sight. The question is what do you care what these people do. Are they actually doing ANYTHING to you at all or are you projecting motivation and attitudes on to them that they might not have.
Here's a good example, a friend of mine has lots of tattoos, he was a tattoo artist for a while and made good money from it but wanted to do other things. He's actually fairly shy, doesn't date very often and wouldn't say boo to anyone. We get on a bus and this old lady sitting behind him starts huffing and puffing occassionally. We have no idea why, we're talking a bit but she couldn't have over heard anything we said over the engine. Anyway, as she gets off and passes by us she quickly turns to him and says "You're not scaring anyone you know!" and quickly hurried off.
Now clearly she's mad, making assumptions, but we ALL do this. So this guy hit a nerve and I'm sure you've got an image of what he looks like in your head, and how he behaves and what he's like and you're splashing all kinds of horrible attributes all over him when in fact you probably know very little about him.
So ask yourself, why are YOU angry about it.
Good luck.
