Jack Rabbit is an obvious parody of James Bond, seeing as how his voice is an impersonation of Sean Connery (the first person to play James Bond), when he's first introduced his introduction is just like James Bond's, and his main quote, "Rabbit, Jack Rabbit.", is also a parody of James Bond's main quote, "Bond, James Bond.". The fact that he's a "womanizer" proves this too.
It is implied that in The Wrong Stuff, Kitty and Jack used to be a couple once Jack mentioned "We can go to our old stomping ground", and Kitty replies "You mean that Italian place?"
His hairstyle strongly resembles that of Danny Fenton and Timmy Turner, both characters who are created by Butch Hartman.
In Freaky Spy-Day, Jack had slightly different looking eyes. He actually had visible pupils.
It might be hinted in Freaky Spy-Day, Jack still has the money he got from the villains that he worked for in exchange for their secrets.
It is suggested in both episodes (The Wrong Stuff/Freaky Spy-Day), that Jack is indeed a vegetarian. He is never seen eating any form of meat products, which may also be due to his species since rabbits eat mainly vegetable based products.