You Had One Job, Fíli
A Slip of the Tongue: When he doesn't tell Kíli the hobbit's name is actually 'Baggins'
Mind Your Manners: When he doesn't tell Kíli it's rude to wipe your boots on someone's mother's dowry chest
Running With Scissors: When he hands freshly sharpened blades to a hobbit who immediately takes off running with them.
I'm Not Saying the Ponies Are Gone: But the ponies are gone.
Not At the Table: When he doesn't tell Kíli not to talk about his bowel habits at the dinner table, and Thorin has to kick him to make him shut up.
Bad Company: When he lets his little brother go on a Quest to reclaim a homeland and slay a dragon with a burglar who's never burgled, a Wizard who's never killed a dragon, and trusts his little brother's life to the word of a weed-smoking Wizard on a bunnysled who's covered in birdshit.
Eat Your Vegetables: When he fails to make his younger brother eat well in addition to preventing a food fight in the cafeteria.
Dude Looks Like a Lady: When he laughs at his younger brother instead of supporting his newly discovered bisexuality.