I liked that Marshall wasn't ready/willing to take back Lily (yet). And how much did Alyson Hannigan's repeated line there remind me of Tara's "Can you just be kissing me now?" (BtVS Season 6)
Barney: "You just checked out Robin's ass."
Robin: "Hey, tell him thanks. I felt like I was having a bad ass day."
Lily: "It's a great ass."
Robin: "Lily's back in town."
Ted: "And you let me go first?!"
Marshall: "I'm a third-year law student at Columbia, so if the workload really does kill you, I can probably get a conviction :) "
Ted: "Okay, we're way past truth-telling Lily..."
Marshall: "But you can never ask me why."
Lily: "You gave me chlamydia, you jerk!" [Then.] "You gave my twin sister chlamydia, you slime!"
Barney: "Well played, Erikson, well played."