Right after the two main characters chug the beer from the fridge, they light up a joint. When the camera switches angles, both bottles are full again. Camera switches back, they're almost empty. This goes on quite a few times.
At little Joe's birthday party, a cake appears, then disappears from the table between shots.
When Mert gets in the hot-tub with Spanky and the girls, the jets in the tub are on, but when the camera switches to a wide shot the jets are off. They're back on for the closer views. This happens repeatedly.
The two girls next door to the boys live on their left side. How is it then possible for the boys to go out the window and go RIGHT to look into the girls' window?
When they're driving the hookers, one of the guys says "Is that a cop behind us?" and we hear a siren. We have a pretty clear view out the back window for a long time before they pull over though, and there's no police car or motorcycle anywhere behind them.
Spanky and Mert are riding in the car with the hookers, and when Princess says "Your dick is sticking out like a spear," out the window you can see the car is going in reverse for no apparent reason.