Plot hole: They're in the Clam complaining that they can't drink when they make the revelation that Brian can because he's technically 56. But Quagmire should be able to drink, as in a much earlier episode, he's revealed to be over 60.
Suggested correction: Quagmire considers the rest of them to be his best friends. He isn't drinking because they can't drink. He is complaining because since his friends can't drink - he won't drink, so he is still pissed.
It's still a plot hole considering Quagmire's age. I think the writers messed up big time.
Plot hole: Stewie gets out of the car seat and goes back to bed, leaving the blanket at the bottom of the seat. When they get to New York, Lois goes to get him out and realises he's gone. But when they started the trip the blanket was covering the entire seat to make it look like Stewie was still in it. So who ever "covered" him up knew he wasn't in the seat before they set off. (00:13:45)
There's Something About Paulie - S2-E16
Plot hole: If the groom didn't know who Lois was but had a picture of her, how could he have known that she was at the wedding so he could place the bomb in the blue sedan? If he had put the bomb in their car while they were still at home, they both would have been blown up. So this means he placed the bomb in the car at the wedding. He didn't know however that Lois was there until the end, where he caught up with them and told them not to start the car. Had he known earlier, he wouldn't have been arguing with his bride about the hit occurring during their honeymoon. (00:20:05 - 00:21:35)
Plot hole: Brian bets Stewie about being at high school for a week. However, this was before Peter's stroke, and before the fire at McBurgertown. It would take at least a few weeks for McBurgertown was rebuilt, then Peter had his stroke, and then Lois tells Chris Peter's stroke was 3 months ago. After this scene, Stewie tells Brian he has lost the bet. However, the bet would only last one week.
Stewie, Chris & Brian's Excellent Adventure - S13-E7
Plot hole: When it is revealed that Chris's teacher was never born, Teacher Doug introduces himself, despite the fact that if Chris's teacher was never born, Doug would already have been teacher for the entire year, and therefore all of the students should know him and he would not have to introduce himself.
Plot hole: As evidenced by the big bar room shootout, even if they couldn't die in this episode, wounds would still show up on your body (if shot with a gun, there would still be a hole). So, when Peter jumped off the building, when he hit the ground he should have been reduced to a fleshy puddle, even if he weren't dead.
The Former Life of Brian - S6-E12
Plot hole: Brian has a 13-year-old son. Not possible since Brian has only lived 7 years.
Plot hole: When Stewie and Brian are at the diner Stewie says he negotiated a deal with the mob by telling them he convinced Mort to give him his flash drive with the info to put the mobsters in prison. When they actually meet, Stewie tells the mob guys the flash drive is "his" and that he bought the coverage. Then he says his address is on the drive so they can mail it back to him. The mob guys didn't realise Stewie lied about whose flash drive it really was. (00:15:40 - 00:19:00)
The Cleveland-Loretta Quagmire - S4-E5
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.
Plot hole: Peter and Lois board the cruise ship without any luggage.
Plot hole: Stewie sets a trap for whoever is stealing his candy. He ties a rope around the table leg but doesn't tie a knot, he just wraps it around the leg. There's no way it would stay suspended.
Plot hole: A man buys Rupert at the yard sale. As soon as he walks out of view Stewie walks over and sees he's missing. He would've seen this happen.
Plot hole: Brian says he spent all his cash in the restaurant yet no one even ordered any food.