Fiona has a lot of disdain for Frank. That is evident in this Shameless scene.
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Fiona ends up lying about an incident involving road rage on Shameless. "My Oldest Daughter" is the second episode of the show's fourth season.
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Shameless Season 4 Episode 2 Quotes

Carl: Ew cankles.
Frank: Like a teenage lacrosse player on the rag retaining water.

You'll have to excuse him. Puberty has turned him into a barbarian.

Fiona [about Carl]