The convenience store is usually called "Maxi-Mart", but in a few episodes the name is "Quik-Mart."
When the music video for the Power Station's cover of Get It On (Bang A Gong) was shown, the album it is from was incorrectly listed as "Electric Warrior." This song is actually from the Power Stations' self-titled album. ("Electric Warrior" is not a Power Station album, but rather a 'T. Rex (I)' album - the band who performed the song originally.)
Sometimes when Beavis and Butt-head are sitting in class you can see through their heads.
The show's disclaimer originally had the following typo: "... the the little weinerheads make us laugh." This ran for more than 2 weeks before the extra "the" was removed.
While Beavis enters his Cornholio phase, in at least one instance he claimed Lake Titicaca was in Nicaragua. It's actually on the Bolivia/Peru border.
When Mr. Herrera says "Como es Juan" to Butthead for the first time, he is facing Beavis.
When watching a Van Halen video with Sammy Hagar singing, Beavis and Butt-Head say something like "how could they fire Van Halen from Van Halen!?" in reference to David Lee Roth's parting ways with the band. However, David Lee Roth is NOT a member of the Van Halen family (though this may have been deliberate to show their stupidity.)