after match teams all report me for afk...
Their reports aren't going to do anything if they aren't true. You didn't get punished for it, now did you?
and report system is semi useless. works at times but not always.
I have been told to kill myself in game and not a single thing has happened to em
How do you know? You only get a notification when your report triggered a review and punishment. If their next game is the one that triggers the punishment then you will never get it, but your report still contributed to it. Saying things like that is bannable for the first offense, so no, they don't really get away with it unless it's a one-off thing and they rarely ever get reported.
posting a screenshot of it on forums and being banned myself
Name & Shame/reporting is not allowed on the boards because the people here can't verify your claims. All you do is start a witch hunt that potentially does a lot of harm, whether that person is guilty or not. It also does no good even if the thread stayed up, because the boards moderators are not Rioters; they do not have access to player information outside the boards and cannot investigate or otherwise take action for your claims.
Also, you can say "shit". Cursing is not a problem, it's harassing players that is.