RP you can do it in public, ERP you do it in private. Who does ERP in public violate the user agreement:
3.3 Profanity and Offensive Language... The Game is for players aged 13 and older. You agree to behave accordingly.
The agreement also say:
...If you reject this User Agreement, then you will not be authorized to play the Game...
tl;dr version and/or for who still does not understand:
If you ERP in public you may be kiss your account goodbye (I think it just suffice a report by anyone witnessed your "performance").

Then, you also can be quite unlucky...: some parent see (and screenshot) what you wrote in public chat of their 13 year-old child, and then files an offence at their local police office about it, if you are in the legal age you also may face court. This is extreme but not impossible.