Interjection. Pronounced "BIHD-wuh-toh". Acronym for "but if you don't want to, that's totally okay." Used to soften a request, in case the person doesn't want to do it.
Ryan: Can you help me cheat on the mathfinal, biydwttto?
Annie: Tell me more about that traumatic experience. (Biydwttto.)
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi