Crowning Moment of Heartwarming: In a shameless action flick, they're relatively rare, but a definite one is, when Murphy's dragged out by the Russian mobsters, he and Connor are yelling for each other, and then Connor rips the toilet out of the floor, climbs to the top of their tenement building, and drops it on the guy's head, because he tried to kill Murphy. Then he jumps down after it and lands on the other gunman, not even stopping to think of how easily the stunt could have killed him. If there was any question of how much the two brothers love and care for each other, this sequence answers it rather spectacularly.
Freud Was Right: One of the detectives accidentally says "fag man" instead of "fat man" in front of Agent Smecker (who even comments that "Freud was right").
Ho Yay: Connor and Murphy are very close. Somefans point to the scene where Connor rips a toilet from the floor in a frenzy and carries it up to the roof to drop on his brother's would-be killers when Murphy is in trouble, as well as jumping five stories down to land on an attacker as a sign of their profound love for one another.
Also the cauterization-by-iron scene where Murphy is holding Connor still from behind. They all got gagged to refrain from screaming, which reduces it somewhat... until Connor reaches behind and clutches at Murphy's hair while the camera pans over to leave only the two of them without even the iron in frame. Thus, it is extremely easy to take that scene out of context.
Then there's the hit on the Sick Mob Man, after which Connor puts his hand over Rocco's mouth, and kisses the back of his hand. Which doesn't even make sense in context, unless you count Rocco'simmediatesilence.
Maybe Magic, Maybe Mundane: The brothers and Rocco vs Il Duce. Is it God's intervention that none of the parties involved die in this epic meeting? Or is it simply because it's three self-admitted amateurs, up against a hit man who hasn't been able to actively maintain his skills for 25 years?
The hockey arena is a subtle callback to Greenly suggesting that their mass execution of the mob bosses take place center ice at a Bruin's game because of how public it will be. It's an homage to the passing of his character, as is the line "Thanks for coming out."
Fridge Brilliance: Romeo either was never actually licensed to operate a forklift, or else he was not licensed by a terribly reputable trainer. The entire "drive the forklift full of heavily armed Irish twins into the warehouse" plan fails from the get go because he makes a very fundamental error: Forklift operators are trained to drive the forklift with the forks as low to the ground as possible, both to give them a clear field of view ahead, and also to keep the center of gravity low (hitting a pothole with three tons of cargo hoisted ten feet up in the air is a very good way to get someone killed). Then again, Romeo is, like his predecessor Rocco, kind of a moron at times.
Narm: Special Agent Bloom's slightly lisping southern accent sounds just a wee bit like Truman Capote at times.
They Changed It, Now It Sucks: A lot of people were unhappy that Willem Defoe wouldn't be returning. Then he shows up in the last five minutes of the movie!