The Distance - S2-E1
Continuity mistake: The posters on Seth's walls are different to the ones he had up when he left Newport. Since Seth has been in Portland all summer and not returned home, it's impossible for him to have changed them and extremely unlikely for Sandy or Kirsten to have either.
Continuity mistake: When Ryan and Seth arrive at school Marisa goes and hugs Ryan. As she hugs him she puts her hand on his shoulders as if to hug him around the neck, or just to let Ryan hug her, but in the next shot her hands are around his waist.
The SnO.C. - S2-E5
Continuity mistake: In Series 2, Episode 'The SnOC', we see Zach punching Seth with his right fist. However, when Summer gives him some ice, he covers his left fist with it (which is now bruised and swollen).
The Chrismukkah That Almost Wasn't - S2-E6
Continuity mistake: When Seth is holding the wheel of jobs for Chrismukkah the arrow on the wheel changes positions repeatedly in between shots.
Continuity mistake: When Ryan and Lindsay are making out, Ryan's hands change position in different camera angles, as well as the way Lindsay is sitting when Kirsten interrupts them.
Continuity mistake: While Sandy is singing and they all have their arms around each other, from the front, you see Alex is next to Zach, but from the back, Marissa is standing next to Alex and not Zach.
Continuity mistake: Sandy's hands change from being on the microphone and being in the air between shots while he's singing.
Continuity mistake: At the beginning of the episode, Kirsten and Ryan are sitting at the table. From the front you see Kirsten pick up her coffee cup. In the behind shot you see her put it down and in the next shot, which is from the front, the cup is still in her hand and she's putting it down again.
Continuity mistake: When Seth is eating alone in the restaurant, there is a plate with leftovers in front of him. In the next shot, when Zach arrives, the plate has moved to the top right side of the table.
Continuity mistake: In the scene where Summer is about to leave for Italy with Zach and then realizes she has forgotten Princess Sparkle, she receives a phone call from Seth. In various shots the phone is on top of her hair and under her hair.
Continuity mistake: When Summer screens the call from Seth at the airport, her phone opens without her flipping it.
Continuity mistake: When Sandy meets Rebbecca in the coffee shop to discuss her running away, Rebecca's coffee cup alternates from being down on the table to by her mouth, when you see her from behind, between shots.
Continuity mistake: In season 2 episode "The Risky Business", the top Summer holds changes position in her hands.
The Return of the Nana - S2-E21
Continuity mistake: Marissa's arms change position repeatedly while she and Trey are down at the beach. Also, her bag appears with her, even though she left the apartment without it.
Answer: He means that if Alex has to go so far as to forbid Ryan from seeing Marissa in order to maintain her relationship with her, their relationship obviously isn't working.