Like Urbanyst said PK, you cannot be direct in your insults. Calling someone a straight up faggot is way too direct because the term 'faggot' is derogatory just by itself. Saying that someone sounds stupid is way too direct because the word 'stupid' is also a derogatory term regardless of whatever context it is used in. And therein lies the issue. Because there is absolutely no wiggle room for debate of what you meant by that. It very clearly was meant to be an insult, no ifs ands or buts about it.
If you mock someone though, you could claim your intentions to be different. 'You aren't very bright' obviously means that the other person is dumb when you read it at first glance. But it could also mean that they aren't very happy/upbeat too, or that they literally aren't shining in light or something. See the difference? No words used in that sentence is derogatory by itself. That's why other posters don't get banned.
Another thing, you directly insult the person whereas other insult the idea. Someone says something absolutely stupid, you call them stupid. This is too direct. You need to say 'that idea is stupid'. Because now you are insulting the idea rather than the person. The reason why this matters is because when you insult the person, it means everything that they have said in the past should be disregarded and that everything they will say in the future should be as well (because if they are stupid, that means they can only give out stupid advice or stupid ideas). But if you insult just the idea by itself, it doesn't necessarily mean that the person will never have a good idea, it just means that his/her current idea is a bad one. Not that all previous and following ideas will be, which is what is implied when you insult the person direct. That is the difference between your insults and another person's insults.
Plus, if someone else were to insult, they would explain why, typically using the word 'because' immediately after insulting them. E.g. "You're stupid because....."
Yours tend to be "You're stupid." Next paragraph.
Those two words have a whole paragraph for itself, showing that the stupidity of the person is it's own separate thought and idea, thus emphasizing the stupidity of the person. Yet because it is only two simple words (which usually are bolded or underlined for extra emphasis), it is mocking in the sense that those two words describe every aspect of the person. If someone were to say 'you are stupid because...' it would lessen the insult since using the word 'because' means that if you fix that one aspect, everything you say and have said COULD have credibility again. But you leave your insults in their own paragraphs which completely voids this possibility, even though your following paragraph tends to explain the other person's stupidity.
In short: it's not what you say, it's how you say it. People can read tone through your text more so than others. That's not a bad thing because people read your posts with more weight attached to them. But that also means your insults have more weight to them.