In an interview I read, Mike Judge said that if the boys have any homosexual tendencies, it would be Butthead, and he would be the one to make the advances. This is hinted in the parts of the show when the boys watch a music video, and sometimes, when something “gay” happens on the tv, Butthead will subtly look at Beavis, and then quickly turn back to the tv.
By “gay” I mean something like a bunch of near nude men singing, or a guy singing a love song in a high voice and the like. Basically the kind of stuff Beavis and Butthead would perceive as “gay”, which you become familiar with if you watch the show. (the music videos they watch are as much part of the mythos as the episodes are)
Of course, Butthead would never actually make the move, because the only person who “respects” him is Beavis, and Beavis is well aware of the stigma of homosexuality, ironically taught to him by Butthead himself. But Butthead could never lose face in front of Beavis.
As for Beavis himself, he is oblivious enough that if it were not for social norms being thrown in his face, and by which his character and actions constantly revolve around, he could be gay and not care. Beavis is unique and a black sheep, but unfortuntely he has no backbone and is basically controlled by Butthead, to a degree. But not enough so that his psychotic and individualistic side can’t come out and suggest to us that deep down, Beavis really doesn’t give a shit about much beyond his sorted imagination and desires. (destruction, mostly)