Near the end of Ian's path, Ian comes out to Penny by repeating Mark's coming out scene from earlier word for word; Penny realizes something is weird about the situation.
Phil's sex scene if Mark the wins the trivia contest. Doesn't matter who's on top; both outcomes are hilarious.
Mark smiling for his mug shot in Jed's route. He is even complimented at his nice smile.
Mark attending the party for Phil's dad while completely on the moon thanks to Ian's animal tranquilizers that he thought were antacids.
One scene has you going to Amos' house via bicycle. Upon going to Amos' place, there are three options: Going right leads to Mark arriving at Amos' place in the middle of his erotic wrestling session; Going straight leads to Mark saying not in this game and to pick again; Going left leads you to a small adventure that seemingly leads you to nowhere, which, persisting through the boredom until Mark can barely walk, which in reward, brings him back to normal with an extra 100 dollars in his pocket. Going left again gives you a Death Glare from Mark.
Heck, just Mark riding Penny's bicycle to Amos' place gives you three scenes.
Depending on your sense of humour, if Mark continues to be weird on Amos' route, you'll get one of the weirdest endings in the game ending with a screenshot Mark blowing with a straw on someone's ass.