You could for example filter out posts where more than a half of the words don't check out in any dictionary. But then the autist is going to find another way to spam. *shrug*
Captain Autism has been reading this thread, because the spam has switched from gibberish to dictionary words now, such as lines like this.
Missouri simpleton bedim spittle confect Thompson cable mart ancestry perspicuous
This spammer is annoying on a level known as "fully gay".