Factual error: In the episode, the Titanic is shown to have sunk the same day it left England. The actual Titanic left England on April 10 and didn't sink until the night of April 14, almost 4 days later. Plus they show it leaving from London, not Southampton as it did.
Plot hole: Brian and Peter see Loretta and Quagmire having sex yet, they aren't sure who she's having an affair with. There's no way they couldn't have noticed it was Quagmire - the couch was facing the front door! And obviously Quagmire was on top of Loretta considering the fact that he leans up, says something, then she tells him to get back down here and finish.
Continuity mistake: When we first see Joe's police car in his driveway, the lights on top of the car have the blue half on the driver side and the red half on the passenger side, later on in some scenes the red half is on the driver side while the blue half is on the passenger side.
Continuity mistake: Meg goes to the party wearing a mask without her glasses on. When she's in the closet, her mask is off and she has her glasses on, even though she didn't wear them to the party.
Continuity mistake: When Stewie goes down the stairs in his bed, when he hits the front door, the door opens outwards outside. It always opens towards the inside. Plus in this episode, the door is brown when he rolls outside. Next scene and the other times in the show it's a red door.
Other mistake: During the scene at the rehab clinic when Brian is jogging, Peter asks if he wants to go "mess with the pregnant teens across the lake." Brian says no because "Group therapy, two o'clock." However, the sky looks as if the sun is about to rise or just set. The time cannot be anywhere close to 2:00, neither AM nor PM.
Other mistake: As Joe is driving up to the house, just before coming to a complete stop, you can see that his window is completely closed. After stopping, Peter says "Joe?" Joe says "Peter?" Joe's window is now fully open. Trouble is, Joe seems to be completely surprised by Peter standing there which implies he never saw Peter even after stopping. His window has mysteriously opened immediately.
Continuity mistake: When the black knight appears and says to Peter "What are you doing with my girl!?", there is a pitcher and a basket with a chicken leg on the table. But on the next shot where the camera is facing to Peter, both the pitcher and the basket disappear.
Continuity mistake: When Meg's boss tells her to fire Peter, he has plungers on his nipples. He walks over to Meg and takes them off. A second later his shirt is tucked in without Peter being able to tuck it in. He's holding plungers in both hands.