Matt's continued spiral into craziness was undoubtedly the best storyline in the episode. Christian was completely right in saying that Sean and Julia were so self-involved about their son that they'd rather yell at each other over who was to blame rather than concentrate on Matt himself. And the fact that they then went and slept together in Matt's bed was just ridiculous. As if things aren't screwed up enough for Matt already!
Christian's weird threesome relationship with Kit and Kimber was hilarious, especially his major irritation over the fact that Kit has turned Kimber into a self-respecting, intelligent woman. The scene with the three of them and Quentin at dinner was the comedic highlight of the episode, with Christian and Kit both fighting for Kimber's privates under the table, and Christian's clear disgust that Kit is planning on inviting Quentin into their already crowded party.
Quentin's interaction with both Sean and Christian was plain awesome. Neither of them have come into contact with somebody like him before, and the freaked out expressions on their faces when both discover at different times that he is bisexual were hilarious, especially Sean's reaction to his winking at the frat party.