I think making a player uncomfortable, force someone to do something that is in any way inapropriated or the player does not want to do the dare in any way, that's already crossing the line. And the fact that they didn't stop after then have been warned just makes it worse.
Even if it is a game there is always someone behind the screen and putting them in these types of situations when they do not want to is disrespectful. Those persons should be glad that you warned them about it before a staff member stepped in.
I already played the game here aswell, but nothing like this, the dares were pretty much stuff that even the one that was being dared, would find funny, and being respectfull about everyone and their privacy.
That's like it should be, just like everything else in the game.
Anyway, I think it's great that you made this a topic, this should be helpful when anyone intends to do something like this.