A rosietastic message is allways written by someone named Rosie because they are the only people perfect enough to handcraft them... except in rare cases when chuck norris writes an email, in which case it will allways be defined as rosietastic.
You may want to look up rosie to see the correct definition of how perfect they are.
Person B: Oh... yeah he was up untill 7:30am writing messages to some chick online...anytime i ask him about it he just screams... ROSIETASTIC!!