I always thought of Beavis as being the more hopelessly idiotic of the two, and Butthead's mental inferior in every way (which is saying something). After the show was canceled, though, it occurred to me that Beavis had always been more 'people smart'. He was a pretty nice guy most of the time, and often seemed close to getting some pity sex before Butthead ruined it by being a Jerkass. -Ryan W
This is sort of touched upon in the Christmas Special, Beavis hangs out with Stewart in Butthead's absence, and is seen at a soup kitchen helping out. Butthead calls him a fart knocker, which Beavis finds amusing and repeats; Beavis isn't a jerk like Butthead, he's just a really impressionable idiot.
I think two scenes in The Movie establish that Butthead is slightly more intelligent, but Beavis has a shade more common sense. When they try to read their own names, Butthead is the one who gets it right, although misses the connection to themselves. When they decide to get out of Buddy Grimes' car in the middle of the highway, it's Beavis who makes the observation that "that road is moving pretty fast", while Butthead just calls him a wuss.
The new episodes have Beavis and Butthead watching MTV reality show dreck like Jersey Shore, and commenting on it more MST-style than the kind of meandering they used to get up to. Why? Because they haven't left the couch or changed the channel. They've been doing the same thing they were doing since they were on the air in the '90s, we just weren't watching.
People complained in the 90's about how Beavis and Butthead were a bad influence, and incited kids to imitate the stupid behavior they displayed on the show. Beavis and Butthead were only able to display that stupid behavior because their parents are absent from the show and clearly negligent in their sons' lives.
Because of his personality nobody would hire Bradley Buzzcut for a job where he works with adults, so he has to work as a teacher.
The Running Gag of people being unable to correctly call the duo by their name already makes a bit of sense because who names their kid Beavis, let alone Butthead? But one particular example really makes sense. In the episode where they go to speech therapy, the therapist keeps calling Butthead "Ted." She probably thinks that his speech impediment gives him a Verbal Tic that puts a "Buh" sound in front of his real name (Buh-Ted).
"Young, Gifted, and Crude:" Beavis and Butthead accidentally unplug wires attached to a computer prodigy's brain-enhancing project, literally frying his brain and reducing his intelligence to the duo's. Some of the consequences of this are shown when the prodigy is demoted from the gifted class to general education, where he is greeted by a mob of jealous students; the real horror, however, comes when one realizes that the duo ruined his life by stripping him of his gift.
In "Werewolves of Highland", there's a homeless person carrying various STDs who is arrested for biting Beavis and Butt-Head. The cop mentions that he's been arrested for biting people before. The implications are indeed disturbing.
At the end of "Holy Cornholio" Stewart steals Beavis and Butt-Head's chance to score with a bunch of hot women. It becomes less funny when you realise he's essentially raping a group of delusional women who don't know what they're really consenting to.
What about the fact that the cult is willing to have sex with minors?
Well just think about the fact that the group's leader was an old man and has probably been doing the same charade for decades. But intentional.