The swimming pool used in the skinny dipping scene with Steve (Justin Chatwin) and Fiona (Emmy Rossum) is actually the same pool used in Cruel Intentions (1999), with Ryan Phillippe and Reese Witherspoon.
There was never a gun involved in the UK series, Shameless (2004); the events between Kash (Pej Vahdat), Ian (Cameron Monaghan), and Linda (Marguerite Moreau) happen regardless.
The sweater that Joan Cusack's character makes for Liam is not knitted as she says; it is crocheted.
A homeless man tells Frank that his office was hit by a Cessna plane. This is likely a reference to the 2002 Tampa Cessna 172 crash, which was shortly after - and inspired by - the 9/11 terrorist attacks. Contrary to what the character implied, there was only one employee fatality and no missing victims.