I am so curious to know what kind of personality Gideon Lightwood had before he went to Spain in his travel year. We know he was kind of asshole because Will or Jem (I really don't recall!) mentioned that he was worse than Gabriel (and at time Gabriel was a prideful brat).
It would have been very funny to see a bad boy version of him
Gabriel: I’m not going to fight with you!
Cecily: Why, because I’m a WOMAN?
Gabriel: No, because you’re scary
Cecily: Oh, alright
Gabriel: Has anyone seen my wife?
Stranger: What does she look like?
Gabriel: Well, she has black ha-
Cecily, from a tree: BEAUTIFUL
*after a few dates with Cecily*
Gabriel: Gid, what do you think of Cecily?
Gideon: I think you should marry her, brother!
*later that day*
Gabriel: Well, I don’t know if I’ll regret this sooner or later, but I followed your advice and now I’m engaged to Will.
Gabriel: Did you know you stole something from me when we met yesterday?
Cecily: Sorry, I’ll return your wallet.
Gabriel: You stole my hea- wait, you did what?