Author Appeal: It's a fanfic, so there you go. In particular, red hair, green eyes, and physically well-developed women are at the top of the list. JoJo seems to be in a local cluster of them, and likes it, a LOT.
Can Not Spit It Out: JoJo is reluctant to mention the inevitable separation of her and Cathy when she goes back to school in the second week or permanently, if she succeeds in swapping places with JoJo-A again.
Catch Phrase: Many, with "Did I mention..." at the top of the list.
"sooo" last millenium.
Chess Master: Sebby knows a lot more than he tells anyone...
Ethical Slut: Cathy, although it may just be for fanservice.
Expository Theme Tune: Except for a few standouts, each chapter has the title of a song, and the songs in each section are in the same category, if not sung by the same artist/group. The song relates to the events in the chapter, either by a pun on the title, or the lyrics describing a similar circumstance.
In-Series Nickname/Stage Name: Almost everyone in-story uses a nickname, based on their given name. JoJo, after learning of Cathy's nickname(“Candy”), immediately starts using it whenever they are alone.
Most of the chapters are named after songs, whose titles or lyrics relate to the actions in the chapter. All of the songs in each chapter has a common tie as well, usually all done by the same artist/band.
Suspiciously Specific Denial: JoJo, a devout Christian, seems to have no problem being either a cross-dresser or gay (depending on how you identify her gender). Being bisexual, however...
She also has a list of "fake blondes" - female entertainers with non-naturally blonde hair - whom she prefers. Her list of said women is suspiciously long. She specifically remarks about her attraction to Cathy, who is not a "fake" blonde.
She "prefers" redheads and brunet(te)s...and "Candy".
Averted (slightly) in how she's taken to being (and being called) a girl. She's careful to make the distinction of being "a guy on the inside", as meaning that she thinks like a guy. She'll still try to correct someone who knows the secret, though.