If someone is offended enough to send in a screenshot, then the screenshot will be reviewed. The determination as to how to proceed will fall on HTC's shoulders.
The game is about having fun. Derogatory, inflammatory, abusive behavior does not qualify as fun for most people. Ultimately, it is the person's choice to be abusive or not. If you chose to be abusive, derogatory, and/or nasty, then you made a choice.
People who act in that manner hurt the game and we are pretty sensitive to that.
There is no justification for being abusive to others in the game or on the board.
As to the specific question about what words are ok or not. Do you use 'tard' to be abusive and/or derogatory (i.e. mean spirited)? Or is it used to poke fun in a light hearted manner?
It is about context. No one can answer whether or not a word is ok or not. If you say it in anger, then you probably are being abusive or derogatory. All we can do is take it a case at a time.