Imagine Levi is actually trying to be friendly most of the time, he`s trying to playfully shove someone and to them he literally just punched them in the arm. So everyone thinks he`s mean, but he`s just rough-housing and then Eren comes along and Levi`s trying his best to make friends cause he really likes him, and unknowingly just pushes him around, but unlike everyone else Eren just laughs because he`s lived with Mikasa his whole life and gets what Levi`s trying to do