Hooper_X
Upon further consideration, "Funk Dat" is probably number three.

Hooper_X
WAIT NO "CALIFORNIA" BY WAX

Camonk
Whatever that song is by Korn where Beavis goes all art-magazine music reviewer.

Whichever the hell video it is where Beavis tells Butthead to shut up and Butthead goes, I'm gonna pretend I didn't hear that, then Beavis mocks him and kicks him in the balls. I wish I could remember which video that is and find it.

Gimme Somethin' For the Pain by Bon Jovi, "SHUT UP BUTTHEAD BON JOVI RULES!"

DAMMIT PANTERA THIS BEER IS WARM
YOU TREAT YOUR STEPMOTHER WITH RESPECT PANTERA
AAAAAAW IS THAT A TEAR I SEE? IS DADDY'S LITTLE GIRL UPSET?!

KnowFuture
Favorite moment is still the one where....Pavement, maybe?...all do this jerky puppet dance in their video and Butthead likes it because they're all dancing together then Beavis makes fun of him for liking it when dudes dance together.

That or MC 900 Foot Jesus "If I Only Had A Brain", the source material for at least one drunken prank call before there was *69 and caller I.D.

Hooper_X
WAIT NO GRIM REAPER

Camonk
"That's not Wolverine, Butthead. That is NOT Wolverine!"

Honorable mention for: "YOU'RE NOT TAKING A DUMP YOU'RE JUST HANGING OUT IN HERE!"