The McPoyles take their revenge against the Gang from the events of "The Gang Gets Invincible" episode.
Contains numerous Die Hard references: the broken glass, the walkie-talkies, the vents, Frank's dirty undershirt, taping the gun to his back, yippee kayea Mr Falcon, and dropping the McPoyle off the roof.
Frank's line when he pulls the gun on the McPoyles ("Yippee-ki-yay, Mister Falcon") is a reference to the infamous censorship of Bruce Willis's line "Yippee-ki-yay, Motherfucker" in the edited-for-TV version of Die Hard 2 (1990).
Kaitlin Olson's little toe was broken at the time of this episode's shootings, limiting her movement throughout.
The McPoyles barricade the door from the inside, but Paddy's pub front door opens out not in, so barricading from the inside wouldn't do any good.