Here's a character who, in her first incarnation, wasn't annoying at all - and then for some reason the writers decided to throw out all of the work they'd done developing her in the original Kick-Ass movie when it came time for the (very terrible) sequel. So Katie Deauxma is the frankly gorgeous object of Dave - "Kick-Ass" - Lizewski's desire, a girl who originally saw him as a gay best friend and then - upon realising he was a famed crime fighter - decided to sleep with him. Uh, questionable morals aside (?), when the first movie ends, they're a nice couple. Cut to the sequel, then, and Katie Deauxma's personality has morphed considerably; gone is the cool, sexy, understanding girlfriend who stuck by Kick-Ass through the traumatic events of the first film, replaced with a total b*tch who dumps Dave the minute she suspects he's getting it on with Hit-Girl - without any evidence at all. The frustrating clash of personalities and inconsistencies on show here renders Katie's character as downright annoying. She acts completely against what's been established - and even implies that she's been cheating!
