Dunno if that was the right thing to do, but good for the MC, he acted because he didn't like the situation.
It's not because of the girl herself, just the MC's own standard of acting if something pisses him off.
I don't know the elf's situation (lost the war, has a sister to protect, not considered human, etc.) but at the moment in manga, I don't give a fuck about her, if she can't stand up for herself she has no right to complain.
Edit: btw how is it possible to be such an obnoxious person in a public place? Being a shitty person and acting shitty in public because you are shit are two different things