By the mid-1970s "Asshole Buddies" had lost its primarily military connotation and became a slang term, more commonly used in the American South than in other regions, to denote two very close male friends who have come to know each other intimately, though not necessarily sexually. Even if they are having sex, they may nonetheless identify as straight.
." Lonnie and Joe Bob? You hardly ever see one without the other. They've been asshole buddies for years."
During WW2, sex was hard to get, and masturbation and fellatio were totally unacceptable practices. But in a foxhole environment asshole buddies could sodomize each other, in turn, without problem, as long as it was kept on the down low.
I get along pretty good with Pvt X. We're asshole buddies.