I love the informality of this one. Fiona makes it look so casual and everyday. I wouldn't be surprised if her left hand is jauntily placed in her jacket pocket.
The bitch-slap one liner is worth its weight in gold too. There needs to be an accompanying cliche for it to be a true bitch-slap. Fiona's one-liner here (something like "You've interfered in my life for the last time") makes me smile when I think how blatantly untrue it very quickly turns out to be.