Erica slapping Harold, it's quite a major event both in-game and for the series, it even got a color page in the light novel, the mangaka did pretty good depicting the event, with the novel author praising it.
EDIT: You can actually see a version of it in the character sheets drawn by the mangaka (See Chapter 7.1)
If you haven't really noticed it yet, whatever he actually tries to say, turns out... poorly, rudely ,annoyingly or straight up evil.
As for other reasons... he wants to maintain the 'original plot' as he knew it to some degree.
@JanQuadran16 He was reincarnated into the villain of the story, also if you remember from earlier chapters, he cannot control his speech. Anytime he tries to say anything, it comes off as incredibly disrespectful no matter what he does. The world basically gave him a filter so that he would still talk like the real Harold. Can be pretty damn funny at times. It is only in specific situations that it switches to respectful, but I don't know if I remember that part right.
Well, if you've got someone who speaks harshly, but acts kindly (to those who actually think about the situation) but wants to appear strictly... well. Isn't that really the basics of a tsundere?
DAMN IT! I forgot all their memorable events at this time don't really happen in chapter 8 but a little later, but the mango is so diddly dang slow. It's only 1/8 as slow as the novel itself but still, so diddly dang doodle dooply SLOW