The three passwords to Cartmans basement are "Fuck You Mom", "Find Scrambles Fast" and "No Girls Allowed". The password to Butters' Chaos Lair is "01234567". The password to the back room in the church is "Kneel Before Jesus". Imputing any of them before discovering will force the game to think you are cheating.
Cartman is the only main character you do not get an actual selfie with in the base game. You can however get a selfie with him in the From Dusk to Casita Bonita DLC.
Originally Trey and Matt wanted to have the game be titled "Butthole of Time"
Mr. Garrison and Principal Victoria do not appear in this game. Also, despite leaving the show, Officer Barbrady appears in this game and is only available to take a selfie with you.
You can actually get two selfies with the same person and that's with Wendy. One with her at Bebe's house and the other with her at the Freedom Pals base as Call Girl.