The hero's acting wasn't quite good enough to fool most people, and his inebriated behavior was so fake that if this had been a movie, the director would have already kicked him out of the set.
Of course, this was not a movie, and there was no one to stop Amos from doing as he pleased. Even if there had been a few 'well-wishers' who didn't want to see Emilia humiliated, they still had to think twice before offending someone like Amos so directly.
And this short hesitation was more than enough for Amos to flawlessly execute his plan. Of course, even if someone had managed to squeeze out a warning, he would still have succeeded.
As he finally 'stumbled' on his own feet and the glass was sent flying towards that villainess he hated so much, Amos felt a feeling of elation and relief in his heart that he hadn't felt for a long time now.
'This is it… this is the feeling! Only when she's suffering is the world right…'
