I know right?

He may or may not have insinuated something about Lia behind her back, of course not to her face, and Atticus may or may not have overheard him call her a rather specific name that he knows pisses her off, so he got pissed off for the both of them. There is a reason Lia is not allowed around Darren.

Oh well of course, Mitch is much prettier and not a jerk. :)