my brain is melting out of my ears

Think about it, they go around, they create chaos wherever they go, butthead has a cleft lip.... it all connects somehow.

1. Superstition surrounding Cleft Lip/Palate

In some parts of the country, being born with a cleft lip and palate can signify
several things in religious beliefs. Those including such as consuming rabbit
meat while pregnant, traversing under the broiling sun, punishment for
breaking laws of the religious type, or even being born under a solar eclipse
can be cause for one to have cleft lip/palate 1[angkorhospital.org]

Hearing that, and looking at Mr. Butthead, doesn't that strike one as kind of
odd that one of such whimsical and horny behavior?
In season 6, episode 8, it shows what the world and life in Highland would be
like without Butthead, and it shows that everything is better, even Beavis is
shown feeding the homeless soup. A normal human could never stir up this
much trouble, and (if you're superstitious in this manner) the cleft lip and
palate could be an indication of something darker at play here...

2. The opposing force to Adam and Eve, sowing destruction instead of creation

In The book of Genesis, in The Holy Bible, it states creation was finished off
with 2 perfect creations, in God's image, Adam and Eve. They were tasked
with naming the animals, and tending to gardens, basically making sure that
all of creation was well maintained and cared for. Just as ying MUST
have its yang, Adam and Eve's is ying as Beavis and Butthead are yang.
Instead of naming animals, they destroy them, shown in Season 1, Episode
1, with them playing baseball with live frogs. In Season 10, Episode 9, they
are seen destroying a garden and planting "cigarette seeds", which are just
cigarette butts, instead of caring for it like Adam or Eve. Beavis and Butthead
have been shown terrorizing Stewart as well, destroying his stuff and getting
him in trouble as they do best. These are not ordinary teenagers, they are of
the devil.

In conclusion, Beavis and Butthead are inhabited by fallen angels of the Bible, from the cleft lip superstitions, to the constant agony and grief the duo causes, we must be diligent that our youth end up not like the likes of Beavis and Butthead.