Prom Wrecker - S2-E5
Plot hole: In this episode all the students say Hollywood Arts has never had a prom before. But in the first episode, 'Pilot', Rex says to Cat after she runs out to tell Tori, Robbie, Andre and him that Sikowitz wants them to come back into the classroom, "Just like you wanted a date to the prom last year."
Plot hole: In the episode where Gabe wants PJ and Teddy to pretend to be his parents when his teacher wants to see them after getting in trouble at school, it is established that Gabe's elderly teacher is short-sighted. When he asks "How many fingers am I holding up" his teacher gives an incorrect answer. However, later in the episode, his teacher spots Teddy on a date at the cinema (movie theatre) and assumes she's cheating/having an affair. How could she have seen Teddy from a row in-front, when Teddy is facing the audience and not the teacher, if she couldn't see how many fingers Gabe was holding up close to her face?
The Muh-Muh-Muh-Murder - S1-E25
Plot hole: Daffy isn't able to escape Porky's house until he gets the keys, but later it is revealed that the reason he couldn't get out was because he was too weak to open the door. If that was the case, the keys shouldn't have been able to help him get out.