"Don't comment on this..."

Here's the thing: it's a public forum. Any one can comment on anything at anytime for it reason. Yes, it may be offensive. Yes, it may have nothing to do with the topic. But, it's still their right to do so. Telling them not to comment isn't going to do anything but make them want to comment more. It's better to ignore them and realize they can do what they want. 
And yes, I know, I'll probably get shit for this but it needed to be said because some people don't realize it.