Bum-ba-bum-ba-bum-ba-bum-bum-bum!
The repeated slapping of Beavis to get him out of his trance was GOLD.
Another calssic video segment(during a Janet Jackson vid):
Beavis(humping the couch): "Aaaaaaaahhhh yeah"
BUTT-Head: "What the Hell are you doing, Beavis?"
Beavis: "Doin' my monkey-boy, yeah!"
Or during Sagat's "Funk Dat":
Beavis: "Question. Why do they call it taking a dump? I mean, you're not really taking a dump, you're leaving it, right? C'mon, FUNK DAT!"