Green’s Dictionary of Slang

(gay) a fellator.

1941		G. Legman ‘Lang. of Homosexuality’ Appendix VII in Henry Sex Variants.
1965		Guild Dict. Homosexual Terms 24: icing expert (n., obs.): A fellator; termed so by the relation of cake icing to semen. (Having its origin in the CCC camps of the 1930’s.).
1972		B. Rodgers Queens’ Vernacular.