Penelope thinks that the crown prince is crazy but to me he's just fearless. I mean his family sent an assassin to kill him, it's not really crazy for him to kill the assassin alhough killing him in the banquet is a tad too much, he might be doing it as a warning to the empress and the 2nd prince. Although raising your sword at people for no reason IS horrible, considering what just happened, he is probably still on guard