The scene in which Principal Skinner says "I am the law" is a reference to the catchphrase of British comic book character Judge Dredd.
The "Pro Movie" video-editing software Bart uses to manipulate audio of President Obama when prank-calling Skinner is based off Apple's Final Cut Pro video-editing application.
The Irish Krusty saying sad stories could be a reference to Angela's Ashes and when he says that his mother filled her pockets full of rocks and walked into the sea. It references when Irish wives lose their husband they commit suicide to avoid responsibilities.
The quote that Romanian Krusty is president for life Krusty is a reference to the dictator Nicolae Ceaușescu, he was removed from office and executed along with his wife Elena on Christmas Day 1989, just eight days after the first ever Simpsons episode was broadcast.
The cup Homer had when he approached to Bart on the pier was a Pig Gulp cup which is a parody of a Big Gulp cup from 7-Eleven.
A number of characters' surnames, as well as first names, are revealed in this episode on THIS list