@ShionSinX @dudewithmagic @grecefar
1st, it seems that he accepts her more as a bratty little sister. He doesn't fully take her seriously. And because he does that, she doesn't give him the respect of a master. Plus, she was suddenly turned into a slave and treated like a little sister, while most slaves are usually taught to treat their master as a master. Our MC on the other hand went big brother on her instead.
2nd, Think about her loyalty. While she does seem to say sh*t, when things count, she's more than ready to risk her life for him...So he values that more than her acting like a little brat. In a world where he can't fully trust anyone, a loyal idiot who can't hide her emotions would actually be a reassuring thing since at least he knows she'd protect him and won't betray him.
3rd, the bin throw is more comic slapstick not meant to be taken seriously (a common joke in anime/manga that you got to get used to; comic violence is never meant to be taken seriously). When reading anime/manga, if the abuse is comic, it doesn't count in universe... Japanese comedy uses slapstick quite a bit, and let's not forget Looney Tunes also uses it. It's like giving Daffy Duck dynamite... it means absolutely nothing.