Green’s Dictionary of Slang

1. (US) one who engages in bisexual oral sex.

1966		Trimble 5000 Adult Sex Words and Phrases 26: bi-lingual (Vulg.) adj. Referring to one who enjoys Oral intercourse with both sexes: a Bi-Sexual Oral Erotic.
1972		R.A. Wilson Playboy’s Book of Forbidden Words.

2. (orig. US gay) referring to one who licks and sucks both the anus and penis of his partner.

1988

H. Max Gay (S)language.