Continuity mistake: In the scene where Josie and Aldys pull up to the court, the sidewalk beside the car is completely deserted. In the far distance, you can see people hanging out and congregating around garbage cans. Then in the very next shot, Guy is suddenly knocking on Josie's window. There's no way he would've had time to make it all the way from the congregation of people to the car that quickly.
Continuity mistake: In the pie-throwing scene, the camera shows the blond football player getting hit in the face with the first pie at the beginning of the contest. In the next shot, there are several pies sticking to the wall as if the contest had been going on for a while.
Continuity mistake: In the lunchroom scene where Josie is telling her coworkers what a "real" kiss should feel like, the amount of sunlight coming in through the window changes between shots. In one shot, Josie's hair and face are matte, but in other shots her hair and the left side of her face is illuminated by sunlight. All the shots in this scene appear to have been filmed at different times of the day.
Continuity mistake: When Josie and the teacher kiss the first time, Josie has her hands on the teacher's shoulders, in the next shot her hands aren't on his shoulders.
Answer: Over the course of the evening, Guy learns that being popular isn't the most important thing in the world and wanted to make peace with Aldys. I think he was genuinely being a nice guy and wasn't in on the prank.