Mary Sue is a girl who enters a television competition with Seth in which he has to lick whipped cream of her body.
Seth Cohen and Ryan Atwood-Cohen meet a girl, Mary Sue, whose grandmother lives in the same guest house where the Nana lives. Mary Sue asks Seth to be her partner in a dance contest broadcast on tv, and he accepts. It turns out the contest involves Mary Sue covered with whipped cream and Seth "licking it all off". While Seth's try "I'm a little bit lactose intolerant" isn't that successful, Ryan's hope is that "Summer hasn't paid her cable bill".
It turns out someone is waiting for Mary Sue: her boyfriend and a entire bible study class. Seth asks Ryan if "we can convince them to turn the other cheek". Ryan's face is definitely skeptical. Luckily biblical boys' revenge just consists in covering Seth with whipped cream. "So I guess those guys really do believe in an eye for an eye". Anyway, even though Seth does not want anybody to find out what happened, unfortunately that might be too late: indeed, while Mary Sue and Seth were doing their performance on the tv contest, Summer was at Zach's and she saw the whole thing on tv.
Played by Jaime King.