When Johnny overhears Lisa talking about how she cheated on him, he decides to record her phone calls. However, the recorder suddenly appears in his hand and a tape is in his chest pocket. It is unclear where he gets either of these items, since this was a decision he made on the fly.
Freshly-lit candles are beside the bed during the second love scene. However, Johnny and Lisa had been drinking for several hours before they went upstairs, and they were supposed to be so drunk they could barely stand.
In the scene with Peter and Mark on the roof, the blue box on the wall keeps changing position. In the shots with both Peter and Mark on screen, the front of the box is shown (easily seen by its yellow/golden decoration) and in the close ups of Mark, the back of the box is shown.
At the coffee shop, Johnny, Mark, and other customers don't pay for their orders at the counter. However, as Johnny leaves, Mark says to him, "It's on me." Presumably, at this shop, customers are supposed to pay before leaving. Mark is not shown leaving.
When Johnny and Denny throw around a football while talking on the roof, one cut makes it appear that the ball is in the air for several seconds, even though they are only standing about four feet apart.
When Chris-R stands in the doorway leading to the roof, the camera is positioned behind his feet and pans to the right. When it pans right, the wall has no "back". The roof entrance goes from having four walls to three, then back to four.
The TV that Johnny throws through the window hits the ground straight down, which is impossible given the angle at which he throws it. Moreover, in throwing the TV he breaks the window, but none of the window glass hits the ground.