The sweater Chris wears for his Bill Cosby costume changes colors between shots.
Quagmire holds a Pawtucket Patriot can while sitting on Peter's front lawn. When the camera moves in, the letter "C" is missing in the word "Pawtucket" on the can, and returns in the next shot.
In one scene, Peter borrows Quagmire's iPod and plays it without being connected to any speakers. iPods don't have built in speakers.
Stewie's AR rifle has a 30 round magazine, but there are 48 spent shells on the floor even though he never reloads.
Quagmire says his grandfather was a kamikaze pilot flying Mitsubishi Zeros for the Imperial Japanese Air Force during WWII. Japan never had an Imperial Air Force; aviation duties were handled by Imperial Navy and the Imperial Army. Additionally, the Zero was used almost exclusively by the Navy and although suicide pilots were recruited from all services the kamikazes are most often associated with the Navy.
It makes no sense for Meg to get highly excited about a little Halloween party make-out session with a teenage boy after she had a ton of full-on sex with hot black adult Jerome in Jerome Is the New Black (2009).