Beavis and Butt-head

Beavis and Butt-head (B&B) originate from the animated MTV show that bears their name. Daria Morgendorffer originated from that show as well, but once she got her own spin-off, B&B never made an appearance on the latter, though they were referred to without being named in an off-hand remark made by Daria in "Esteemsters." in an off-canon canon interview on the CBS Early Show, Daria was asked an interesting question by Jane Clayton.

JC: You made your debut, Daria, on the MTV show Beavis and Butt-head. Do you still keep in touch with those guys?

Daria: I'd like to. But first, they have to figure out that when the telephone makes that funny sound, you're supposed to pick it up and say hello.

In Daria fanfiction the duo make many appearances, both in flashback and in the Dariaverse.

Daria in Beavis and Butt-head

 * “Daria on Beavis and Butt-head” (Outpost Daria)
 * “Beavis and Butt-head and Daria” by CF (Outpost Daria)

Beavis and Butt-head in Daria

 * April 2005 interview with Glenn Eichler on DVDaria, which mentions why Beavis and Butt-head were excluded from Daria episodes.

Beavis and Butt-head in Daria Fanfic

 * “Daria 2007: The Girl from Hope”: B&B are not named as such, but they are obviously the pair responsible for the shootings in Highland, Texas.