When you work at Joe's Pizza there is a chance that it will say "Sewer People ___ tip." This is a reference to TNMT, where the turtles love pizza.
When you go to the very right hand side near the castle and alien/ufo, you can see a creeper, from minecraft, poking its head out of the cliff.
My Spoon is Too Big (Rejected)
On the back wall of one of the buildings on the second island, you can see graffiti depicting one of the characters from Rejected, the Don Hertzfeldt animation.
Stick RPG 1
Homeless Harold can be seen in both Stick RPG 1 and 2.
Skater guy, who gives you his skateboarder in exchange for cigarettes in Stick RPG 1, can be found next to the 711. He claims you lost the skateboard and will give you a new one for a XXX movie.
In Stick RPG 1, Skater Boy dies of overdose of cigarettes,but in Stick RPG 2,he returns alive and doesn't die. The Cocanut Cowboy dies of overdose of cocaine and give the Mobius Strip,which is a reference to Skater Boy in first game. However if you choose play with good karma isn't necessary kill him.
The Most Interesting Man In The World , off beer commercials
When you go to the club in 3rd island,sometimes you can see a girl,that asks "Do you BELIEVE in life after LOVE?",it's a reference to Cher and her song "Believe", the capital letters may be a reference to her voice tone in the music.
The Cocanut Cowboy always sing the song "Dead or Alive" of Bon Jovi when the player give cocaine to him.
Tack Jompson, in the police is a parody to Jack Thompson a ativist who is against violence in games
The Hoverboard , off Back To The Future
Isaiah Musticka , off Old Spice commercials
Your Wife , symbol off bathroom doors
Error , off Legend of Zelda
Tutorial Ted , His last line before the battle is also Dracula's
Teen Cocaine , Talk to the girl in The Club's toilets with high charm.
Vinnie, may be a reference to Sift Heads.
Dr Nick, In medical career you say "Hi everybody!"
Tyler, Chainsaw Club from movie Fight Club
Doctor Home, may be a reference to the TV-show Doctor House
DJ MatchStick McQuick says: "I told you already , im not playing Sandstorm" may be reference to popular scams on YouTube: "Song name?" , "Darude-Sandstorm"
Mr. Schrute and Creed are references to Dwight Schrute and Creed from the TV show The Office, and say things typical of their corresponding characters.