Online, where you don't have the benefit of real-time physical feedback and things like sarcasm and trolling are easy for the gullible to mistake as honest friendship or encouragement leads the autist to believe they are in good company when they act out so they are much more unfettered and go on for far longer before realizing something isn't right when their "stage" is Facebook, or Twitter, instead of a classroom or movie theater where people would quickly excise the nuisance in their midst.
In short, the autists' own lack of personal behavior boundaries gets pumped up to 11 when allowed to run amok online.