"I think it's Japanese for gay." While the Japanese word has no connotation towards sexuality, and usually just refers to guys who have some sort of working relationship (business partnership, tennis partners, wingmen in picking up women, or simply best friends etc.), it can only be translated into English as "partner," and so the homosexual connotations of that phrase have carried over. It does not help that the word was largely popularized in Yu-Gi-Oh as the pharoah refers to Yugi as Aibou, and there is a lot of homosexual oriented fandom regarding that "partnership." Official coinage as a synonym for "gay" by Marik from Little Kuriboh's Yu-Gi-Oh the Abridged Series.