So the meanings are:
1. Useless retard, "retard" because of the "tard" in the word
2. Hetalia obsessed person
Girl Two: No, he's such a hetard
Girl One: A what?
Girl Two: A useless retard
Girl One: Oh...
Girl One: I bought Hetalia plushies and posters and dvd's and etc etc etc...
Girl Two: Wow, you've become a Hetard
Girl One: No! I've become one with Mother Russia!
Girl Two: o_o...