On the Big Island of Hawai'i, down in the lower Puna District,
BTF means Below the Flow. Someone or something that is located below the flow of Tutu Pele's path.
Guy 1: Man, that girl is btf af
Guy 2: Damn bro, why don't you try to date her?
Guy 1: You know what? I think you're right. No more jerking off to hentai and playing dating sims
A person who exemplifies a body crafted by the god's hands to service mankind's ultimate fantasies of beauty and lust. This person is has absolutely no trouble finding sex in any scenario. Everyone wishes to look like this person, and everyone wishes to fuck this person. The person has all exclusive rights to chose their fuck buddy for the evening, because when chosen, you must not turn down the opportunity. If you do, you will be thought of as queer or just flat out retarded. This person is so well versed in intercourse that even a nerdy virgin would turn into a sex master (or at least an intermediate) just by (somehow) having intercourse with this person. You will know this person when you see them; they are the orgasm in your eye.
WARNING: while this person may be BTF, they may not be DTF. (some people are assholes like that)