If I remember correctly, they mention Beavis' dad in at least two episodes Be All You Can Be and Furriers(?). In Be All You CAn Be Butthead says that Beavis' dad was in the navy, he was a seaman, get it? In Furriers, after Daria tells the class about the minks getting 50,000 volts up the butt, Beavis wondered aloud what that would feel like. To which Butthead replied, "Ask your dad". Those are the only two that I can think of.
James Santerre
BH: I think my hair is pretty cool. Scott Ian: I think you look like a dick. B: Yeah you look like a dick, a dick, heh heh