Character mistake: When Peggy and Lupe return to Mexico and Peggy thinks the crowd of people are cheering her on, she says "Por los niños!", pronouncing the "ñ" correctly. However, in several other episodes of the show, she pronounces the "ñ" in the word "español" incorrectly.
King of the Hill (1997)
1 character mistake in season 6 - chronological order
Starring: Brittany Murphy, Pamela Adlon, Mike Judge, Kathy Najimy, Johnny Hardwick
It's Not Easy Being Green - S5-E16
Factual error: Boomhauer's car, Ms. Sally, has a Texas flag license plate on it. These plates were not issued until 1992, but Ms. Sally was driven into the quarry in the late 70's or early 80's.
Dale Gribble: Boil up some Mountain Dew. It's gonna be a long night.
More trivia for King of the Hill
The Man Who Shot Kane Skretteberg - S2-E7
Question: When we first meet Kane Skretteberg, what is the song he and his band are playing in the garage? It is right before they start singing Funcenter over and over.
Answer: If you are talking about the "Thou shalt not do this, thou shalt not do that" song, I'm not sure if a song like that actually exists. Green Day, the guest voices on the episode, might have just been improvising to keep their appearance from being too obvious.