The Glasses - S5-E3
Continuity mistake: When George bites into the onion, you can see the top of the onion is facing up or towards the camera, next to his finger. In the next shot, you can tell the onion has rotated position. You can see the root is to the side, so the top would be on the side instead of up.
Chosen answer: George does mention his brother in the episode "The Parking Space". They actually really never mention anything that contradicts the fact he had a brother though, it just isn't mentioned.