When I think of Yuuichi as an jackass, I think about his scenes with Nayuki, where she gets bullied for no reason at all. If we talk about Makoto, well, like @Pepe said, no normal person would trust an amnesiac who hates you for no reason and has decided to live in the room next to yours the day you meet her. It’s more than justified. Hell, even Makoto tries to play pranks on him every night. I would never forgive her.
Ayu is more a weirdo than anything. She steals taiyaki and tackles him almost intentionally more than once (because yelling get out of the way while running trying to escape from the taiyaki vendor isn’t an excuse).
So, all in all, he is an asshole, but his actions are pretty understandable most of the time.
@Pepe, you are living in Japan. Aren’t random hugs in public places something very embarassing there? Because I don’t know about you, but I would act the same way.