JESS: I’m not gonna fight you, Dean … ‘Cause if I fight you, Rory’s gonna think it’s my fault, so just forget it, okay? Just forget it. Go home. Let it rest.
DEAN: So Rory’s got a nice little hold on you now, huh?
Any ideas that Dean might just be a nice boy who has been pushed to his limits by the shenanigans of Rory and Jess are well and truly put to bed here. In his first confrontation with Jess since he broke up with Rory, Dean shows himself to be mean and spiteful, playing mind games with Jess to try to convince him that he is as manipulated by Rory as Dean was.
Dean seems to take relish in the role reversal that he and Jess have now. Just as Dean had to keep his jealousy and irritation in check when Rory hung out with Jess, so Jess now has to behave himself around Dean, lest Rory blame him.